Audio Systems: Sound quality fading on car audio system, volkswagen jetta gt, kenwood amp

Question
Hi there, thanks for your help on this excellent forum.

1.  1997 Volkswagen Jetta GT 2.0 (Mark III) w/ 83K KM.
2.  I have a Kenwood MP425 MP3 CD Player that puts out 50 Watts x 4 MOSFET.  I just bought a set of Rockford Fosgate 4306 6.5" speakers that are rated at 100W apiece.  For quite a while they sound great even at high volumes with crisp bass, full mids and very clean highs.  However; after about an hour of playing at moderately high volume (22 - 25 setting on the Kenwood), the sound sort of fades into a sort of distorted sound with the clarity fading almost to nothing.  The sound reminds me of the days of using a walkman with cassette, and the batteries fading out.  I know this isn't the case though since I have installed a high powered battery and alternator as well as professional power lines since I am planning on installing a high powered (1000 watt) Rockford Fosgate Amplifier.  

Can you please let me know what I might be doing wrong?  Also if you do know, I wouldn't mind finding a good product that I can put behind the speakers to help get rid of vibration in the door.

Thanks!


Answer
Trever,
Sorry it has taken me so long to reply. My hard drive crashed and I've been in disaster recovery mode for awhile. Anyway, I've been pondering this question, and asking around for awhile and I can't figure out what's going on. The best idea I've been able to come up with is that the Kenwood amp just gets too hot and the quality starts to degrade with it cutting out. However, I've never heard of a deck's amp cutting out. In point of fact, I've never heard of this kind of problem at all. I highly doubt that the speakers are the source of the problem, since the 'fading out' happens with all the speakers. I would recommend that you have somebody take a look at your deck and see what's going on. Also for the vibrations in your door, get Dynamat. It's the most popular product out there and it's one of the best. I'm using it right now. It's a sheet-like material that is applied to the inside of the door itself. It dampens some vibrations, and increases the actoustical properties of the car. If something is loose in the door panel, then Dynamat won't really help - but if you're getting Dynamat, just tell the installers to tighten everything down while they're doing the install.

Best Of Luck,
Alan