Sound, but major distortion

Try another speaker - if it does the same thing your amp is damaged.
If replacement speaker sounds fine then your original speaker is defective.

the distorted sound coming out of your sub-w is actually originating from your audio unit, Have your audio unit check for possible repair

Simply put, burned voice coil. Either too much power can do this or not enough power with distortion. solution- if the sound is clear then its too much power- turn the amp down. If the sound is distorted and raspy- its not enough power and your getting distortion-get bigger amp.

muffle sound in one speaker

The JBL premium sound system has a large woofer in the bottom of each door, a small mid-range speaker next to the woofer, & tweeters next to the front door windows in the corner, & two full-range speakers near the rear seats. The woofer (not sub-woofer) handles all the low end. You can test the woofer by turning the BASS to max and TREBLE to minimum (make sure balance and fader are centered) and put your ear next to each woofer.
The woofer is usually the 1st speaker to have problems after 10 years or so. The outer edge of the woofer starts to degrade. You will usually hear a rattling sound out of the woofer when this happens.
NOTE: If no sound at all out of the woofer (tweeters are OK), you might take your car into a car stereo shop. They can put a speaker on the wires connected to the speaker and make sure your problem is not the radio.
PROBLEM: You can still hear sound out of the woofers but it is distorted
SOLUTION 1: Go to a car audio shop and have them install new woofers. These may cost $30+ each but the dealer cost is over $200 for each woofer (crazy).
SOLUTION 2: More involved but very cost effective. If you or a friend is handy, you can go to www.speakerworks.com and order a new set of speaker outer rings (on the site they are called speaker SURROUND) that will replace the damaged outer rings on the woofers (replace on both woofers). They really work great and your speakers should last for many more years.
Hope this helps.

Sounds like the voice coil of that woofer overheated and melted while it was turned up too far. Now that area rubs on the magnet or pole piece internally and makes noise.

No you generally can't fix that except for a few high end woofer brands that have field replaceable voice coils that you can buy. Most subwoofers physically bottom out and sounds really bad before experiencing thermal damage like that. Sounding bad is a warning sign that it's being overloaded.

Note that woofers have 2 different types of overload conditions that can cause damage.
1. Over excursion from deep bass that moves the woofer cone too far and damages the suspension. This is clearly audible. Proper box design and user knowledge will prevent this.

2. Thermal limit. This is the published power rating that the voice coil can absorb without damage. Things can melt or fail entirely if this is exceeded.

Either of those issues can cause the noise you are hearing. Without a more detailed description of what happened or how it sounds before, during and after this is much detail as I can provide. But.. move the woofer some by hand, do it evenly pushing straight down evenly on both sides, not too far, go about half way through it's normal movement. If it clearly rubs and makes noise internally then the voice coil is damaged or if has some debris stuck in there. Most woofer are not serviceable.

There are many other factors that affect the longevity of the woofer, such as

• Ambient temperature too high
• Limited air flow has inadequate woofer cooling
  
• UV exposure can make the surround material brittle
• Proper enclosure design is needed to acoustically and physically supports the woofer to prevent bottoming out, particularly at the system resonant frequency.
  
• Amplifier distortion can kill speakers even when rated far below the woofers max wattage.
  
  
  

I think you've just answered your own question. It sounds as if you've coned the sub woofer. Meaning you've fractured the bond between the edge of the speaker body with the speaker cone. Or overheated the voice coil and it's distorted and not getting free movement. Excuse the Pun but it "sounds" like you need a new speaker as a replacement. If it's a particularly expensive speaker it can be reconed. A check of the Net for someone close to you will find a company who recones them. If it's a cheaper one then a replacement would be in order.

Your sub woofer is not mean for voice sound...check that you have connected the systen up properly and that you have put the sub woofer into its wn connection..if it is in the right connection the woofer could be blown.also try decrease the midrange hurts on the woofer

sound slike onbord sound took a **** or driver failed go to makers website eneter in your model then driver downloads are ok dl new sound driver test that 1st if no go buy new pcmia card sound blaster makes and get hi end 24 bit sound way better

your memory is low on resources need to increase memory.everything on ur pc uses mem.audio and video devices use an aweful lot.if you have open another program not only will ur audio be distorted but ur other program will be running slow.
correct? need to add more ram.