2001 Sierra 5.3 ltr. automatic tranny There is a whining sound inside the cab. It seems to be coming from under the dash. I have turned off all accessories. The sound continues in park, neutral or drive. It fluctuates directly with the engine RPM. I have been under the hood and on a creeper under the vehicle. I cannot hear it outside the cab, probably because of engine and exhaust noise. It started this winter, I have had several occasions where Auto 4wd and 4hi were used, but only on surface streets, not offroad. There are no performance problems or other sounds that I think are related. While under the hood I took a stethascope to all bearings that I could reach. The only bearing that sounded rough was the rear alternator bearing, but it did not have the same frequency as the sound inside the cab. It starts within a few seconds of the engine being turned on and continues the entire time the engine is running. The truck has 82172 miles, I run Amsoil in the crankcase since the odometer turned 500 miles. The only problems I have had with the truck has been a bad water pump and a seized park brake cable. I have been diligent about preventative maintenance. The only maintenance I have not yet done is a tranny flush and new fluid and filter. Please help, I am extremely frustrated!!!

Hello
first ya need to remove the drive belt. that will eliminate all pulleys and pumps..

if the noise is gone you then know its a pulley or water pump issue.

if the noise is still there you know its drive train. that would mean timing chain, torqe converter, or trans front pump.

have you replaced your timing chain ?
have you performed trans flush/ filter change ?

when driving down road does hum change pitch when you slip it from drive into nuetral going about 40mph? = trans issue

check timing with a light to see if you have chain stretch if its out of time = chain issue

good luck

I had the same problem with my sisters blazer .i replaced the alternator and problem solved. alternator capacitor is defective.

Hello,

Just buy a used altenator for 40 bucks that will fix your whole problem and its an easy simple fix but its definitly your altenator... its not woth trying to repair the old altenator because its more trouble then what its worth diagnosing every little thing,

thanks,
Steve

Hi! You said that the alternator is feeding back through a speaker (That was a very good call by whoever suggested it). Also, you stated that the rear alternator bearing was starting to make noise. GM alternators are notorious for dying prematurely (almost always because of the rear bearing loosing it's lubrication) and leaving you you stranded. With no alternator, the fuel injectors don't get enough power to fire correctly and the engine dies. Since you already know that the alternator is going, and trust me that if you can hear it - it's going, I strongly suggest replacing it now (it will save a tow bill atleast).
As far as the feedback through the speakers, I suggest a cheap 'alternator and ignition noise filter' available at your local auto parts store or J.C.Whitney.
If you still have a problem after doing these things, the next place I'd look is the transfer case (front output bearing) or the front differential bearings. Good luck.

Www.gmpartsnetwork.com

They have the best prices.

Resister GM# 89019089 AC Delco# 15-81087 approx $27.00

There are two solutions to this, since it is somewhat new.  A) replace the alternator, and/or B) get insulating spark plug wires, or both.  Clearly your sound system is picking up engine noise.  Typically this is due to the ignition system, not the charging system, since the voltages are significantly higher in the ignition system and thus the eletromagnetic fields are greater.  An additional option is to put an inductor inline with your sound system to filter out the high frequency signals.

This covers almost all possible causes Alternator Whine The following steps will aid you in locating and correcting a ground loop problem.

1. Verify that all audio levels are set properly.
2. With the system turned off, unplug the RCA inputs to the amplifier.
3. Start the vehicle and turn the system on. If the noise is gone go to step 8. If the noise is still present, it is coming from the amp or the speaker wiring. Continue.
4. Turn the system off and disconnect the speaker harness.
5. Start the engine and verify that no noise is present. In a few rare instances, I have actually heard speakers reproduce noise without being connected to an amplifier. This noise was being induced by power cables that were very close to the speaker wire. If you do have this type of noise, reroute the appropriate speaker lead and go to step 3.
6. With the speaker harness still disconnected, check to make sure there are no shorts between the speaker leads and the chassis of the vehicle. A shorted negative speaker lead will create a ground loop by establishing a second audio ground reference point. If you do have a short, trace the wire out and repair it then go to step 3.
7. With the RCA inputs and speaker harness still disconnected from the amplifier, use your VOM to measure from the shield of the RCA jacks on the amp to the chassis of the vehicle. This reading should not be a direct short (100 ohms or more is acceptable.) If this reading does indicate a direct short, you might have a defective amp and should contact the manufacturer for verification. (Note that there are a few "inexpensive" amps or boosters on the market that have their audio ground and electrical ground commoned internally. For units of this type, the information in this article will be of very little value.)
8. If you've made it here, you know that the amplifier and speaker wiring are okay.
9. Connect the accessories in front of the amp (crossovers, equalizers, etc.) one at a time and check for alternator whine. When each device is tested, there should be nothing plugged into the input of that device. In this way, we will work toward the source unit piece by piece. Be sure to turn the system power off before connecting or disconnecting any cables or accessories.
10. Repeat step 9 until all accessories have been tested.
11. If a particular accessory is causing noise, try disconnecting it's power ground wire. Go to step 9.
12. Now it's time to connect the source unit. Do that now and test for noise.
13. If noise is present, try unplugging the antenna. If the noise goes away, you will need to use an antenna isolator. This little gismo opens the shield wire of the coax to eliminate the ground loop caused by the ground at the antenna.
14. If you still have noise, try connecting the source unit's ground wire in another location,. preferably as close to the source unit as possible.
15. Does the noise vary in amplitude when you adjust the volume control? If it does, the problem is probably power line related and not a ground loop. If this is the case, run the source unit's B+ (yellow) wire directly to the positive terminal of the battery. If this doesn't do the trick, you will probably have to use a power line filter on the source unit's B+ (Yel) and Ignition (Red) wires.

1. Make sure you are using resistor type spark plugs and resistor type plug wires.
2. Determine where the noise is coming from. If the noise is a popping sound that occurs 2 or 3 times a second, you probably have a loose or bad plug wire. First, make sure that all plug wires are seated properly. If this doesn't do the trick, you may have a bad plug wire. Usually this occurs due to a pinhole in the insulation of the wire. Whenever the plug wire is energized, an arc jumps through the pinhole to the chassis of the vehicle. Replace with silicone resistor plug wires.
3. If the noise is a buzzing sound, the problem is usually associated with the points, distributor, or coil. Try replacing the condenser on both the coil and points. Make sure all plug wires are seated properly in the distributor cap. Additionally, you might try adding a 2200 uF cap from the positive terminal on the coil to chassis ground.
4. Don't use the fuse block in the vehicle to derive power for the source unit. Run the Constant Hot B+ (memory) wire directly to the battery's positive terminal.
5. If you still have noise, it could be occurring because of induction. Try pulling the source unit out of the dash and check for noise. If the noise is eliminated, try rerouting any wiring harnesses that are close to the deck. If this is not possible, try using self adhesive metal shielding.

I would suggest removing the resister block that controls the heater fan and see if that removes the noise

It is a bad ground if the alternator is causing noise like that. You have the stock radio in the truck?

No, you don't not need to replace your alternator. In fact, there is a very small likelihood that it would help in the least.

The problem you're experiencing is often referred to as a "ground loop." As long as the stereo system is stock, the problem should be fairly easy to fix. If you've added an after-market deck and/or amplifier, then it will be a little harder to track down the problem. But, we'll get it squared away one way or another.

For now, I'll assume your stereo system is stock.

The most common culprit of ground loop whinning is an unproper head unit ground. Many

It indicates that there is a problem with the alternator.also check the belt and front bearings as it might also cause this the other way.

Behind the dash there is also the power steering system, when power steering starts having trouples, it may still work, and you get a whining noise from PS pump and belt.

If problem is power steering, "the sound fluctuates with the RPM of the engine".

First check the regular serpentine belt, and try pushing more the tensioner, that is the most common cause for whining noise when "the sound fluctuates with the RPM of the engine".

Have your alternator checked it can be backfeeding current and this would cause the noise you speak of coming from speakers.

It might be a central differential bearings
Also have a look at alternator one more time
Around 1000 RPM is about the point where an alternator is really catching up and putting power into the system instead of just holding even with the engine's computer, injectors, etc. demand for power. So that might indicate front bearing issues starting, or possibly an open-failed diode making noise, the "noise-emitting diode". It could also be irregularities (as in cracks and pits) on a belt, but a visual and finger-rub inspection when everything is turned off and all sets of keys are in your pocket will find that.
Good Luck

Welcome to Fixya! The only thing that comes to Mind would be the Blower motor and Maybe the Door and Ignition Buzzer could be Malfunctioning. Check these and let me know so that we can go on if needed!

Inside the alternator is a noise surpression capacitor, this filters out this whinning when it is working, i suspect the part is defective, u can mount an external filter capacitor either at the radio power supply or add it onto the back of the alternator, radio shack can help u out with install instructions and the filter itself.