Noise in rear wheel of Toyota Tacoma

If grinding noise is heard coming from front side, lift up both the front wheels and rotate the wheels one by one to listen to the sound, if any. If a noise is heard, replace the front wheel bearings as a set.
If the front wheels do not produce any abnormal noise when rotated, lift down the front vehicle. Lock the front wheels with blocks, release the hand brake. lift up the rear wheels and try to listen to the abnormal noise. If the noise is heard, replace the differential bearings and seals. Top up the differential oil to the mark.

Could be your belt is stretched and needs to be replaced,can't tighten cause it's done by tensioner.Here's a link to the belt replacement guide.To check out noise,open hood,stand at engine,have someone start,listen for noise,have person rev up engine and you find where noise is coming from.Also check tensioner.

Sounds like a wheel bearing. Jack each corner of truck in air and grab top and bottom of tire and see how much it moves. If it moves anymore than a little you have a bad wheel bearing.

Take it to sears auto or a good alignment shop and let them check it out. Pitman arm or end links may be going bad.

The drive shaft is inserted into a splined hub. The hub has a bearing that is pressed in, and that may have been the cause.
Very rare. Was there any grinding noise before it fell off ?

2.7L or 3.4L, Extra cab or SR5 Extra Cab or Regular cab, also need an email address to send instructions to (in pdf format) Adobe Arcobat

I don't know how loud the noise is, but its weird that you mention 50 mph. At that speed or above you are keep a constant rpm level. I say this because it might just be your air box loose and the sound of the intake air is making it. A 2008 truck should not have any major problem. Sometimes an alternator will sing or whine but never heard anyone say something is whistling. One other thing is sometimes for some reason ive heard a noise like that coming from the speakers of my car that goes up and down with the speed of the motor, but that was when I was tinkering with speakers and sub outs and amps. Thats all I can think of.

I had a problem with a whistling car after 50 mph and it turned out to be the front window gasket. I put silicone on the trim and problem solved.

Id get a mechanic to look at it. Sounds like a rear end bearing problem. Axle bearings pumpkin bearings.

Without looking at it, you may have one or more of the following:

Rust on the inside edge of the rotor (most common)

Worn front brake pads

Front wheel bearing problem.

Backing plate (behind rotor) rubbing the rotor

These are the most common causes, you can see 1,2 & 4 with the wheel off.

Hope this helps.