mystery knocking sound
 

please, can someone share their knowledge and shed some light on my issue.
2002 996 turbo,
a knocking sound coming from rear.
the sound is best discribed as higher pitch knocking/ tinging.
does not exist from cold start, only when the car heats up, about 5mins of driving.
when warm and in park, in idle, you can hear it,
can also be heard when i accelerate slowly,
but the sound does away when i push down on the gas.
very noticible when i go up a ramp in a parking lot or up a sleep drive way,

i thought it was rusted mounts on the muffler/heatshield.
replace exhaust to new factory OEM exhaust....sound still there.

have gone to 3 "porsche specialist" shops and to only have them say, take it to the dealer...
they all say they hear the sound, its coming from the rear driver side,(inside?) the drive housing.
they also said that it should not be damaging to the car, since the sound has existed since i had the car for the past 2 years.

had bad experience with the dealership, but i might have to bring it in.
also, trying to avoid dealer costs, car out of warranty.

any suggestions/insights?