Speaker 'buzzing' problem

[ml1]

997 C2S 2 months old standard sound package. There is an intermittent 'buzzing' not unlike a speaker with a loose earth wire coming from the front middle speaker. Left it in to the dealer but they couldn't find anything wrong and reset the computer but the sound has returned. Even when radio is turned off the sound is still there and when the car is switch off key removed the sound remains for a few seconds (I assume electronics in car haven't powered down totally). There doesn't appear to be any logic as to when or how loud the noise occurs.
Any ideas on what the problem may be please?

[systech]

I had a similar problem on my Boxster S when I replaced the standard Dash speakers with some coaxial JBL speakers which had quite a long lead for the (external in line) crossover networks. It seems that the cause is electromagnetic coupling into the speaker cables from some of the nearby signal cables in the dash. The cure in my case was simply to reduce the length of the speaker/crossover cable and reroute the cable and the induced noise was gone.

In your case where I assume that you have the standard speakers, you might try and remove the speakers and re-route the speaker cable so that it is far away as possible from any other cables. May not cure the problem but will at least verify whether that is the problem - as you move the cable you will probably find that the noice waxes and wanes.