low frequency, high volume noise through speakers

[philmartin356]

I have a 2006 Boxster, stock, no special options or after market add ons. Yesterday I parked my car in the sun and high temp (mid to upper 80's) while attending a car show for about four hours. Upon starting the car for the return drive home, a low frequency "pounding" or "thumping" noise (much like the sound of heavy bass coming from a car next to you with its sound system turned up) immediately began coming through the speakers. The volume of the noise did not change when the volume of the radio was changed. Upon arriving home and shutting off the car, the noise continued. The noise stopped for no apparent reason several minutes later. Upon restarting the car, the noise immediately returned, and once again continued when the car was shut off. The noise seemed to stop very shortly after the car was locked with the key. Upon unlocking the car but without starting the car or inserting the key, the noise returned. Again, the noise stopped within 5 seconds or so after the car was relocked. Locking the car is the only way I have discovered to get the noise to stop. It has been suggested to me that I might have a faulty amplifier (part number 987.645.331.01, image attached). Further, it was suggested that the amp has an updated part number, which I assume means Porsche no longer uses my original amplifier but has replaced it with an updated model. Finally, it was suggested that this is a repair that should be done at a qualified Porsche repair facility due to the new amp needing to be coded to the vehicle. I have several questions:

Has anyone had a similar problem? If so, what was the problem and how was it solved?

Does the faulty amplifier diagnosis sound reasonable?

Would there be any problem with me disconnecting the large cable the amplifier and using the car as I determine a repair strategy?

Is this a DIY repair, if I am able to get a replacement part?

I live in central Iowa. The nearest Porsche dealer to me is in Omaha, so it's not a trivial trip to deal with this through a dealer.

Thanks in advance for any insights anyone can offer.

Phil Martin

Ames, IA

phil.martin.sc@gmail.com

[slowhand220]

My 2006 Cayman started doing the exact same thing one week ago today. My dealer diagnosed it as a bad amp. I have been searching the web for a used amp. The radio works without the booster amp hooked up, so there should be no problem. I am driving mine with the booster amp unhooked now. I hope to replace the amp early in 2012.

Please visit my YouTube channel for a video of the problem.

http://www.youtube.com/slowhand220

Edited December 23, 2011 by slowhand220