Right, I bought my 8L 2 weeks ago. It has an APR chip in it. On the drive home it felt fantastic - bags of power and a surge of torque at 2800 rpm.
Then near home I noticed a new found hissing / whooshing/ sucking noise from the engine bay. The car definitely felt as if it lost power and torque.
I took it to a specialist and he did a smoke test. No problems he said. He cleaned out my MAF and cleaned out and pulsed my N75 valve. The car definitely felt quicker but it's still not as quick as it was - mainly it's not giving that huge power surge at 2800 - it's more of a long, smooth push of power as apposed to the rapid boost rush like before, even though it's still very quick. Hard turbo rush seems to be about 3500 now.
Nothing came up on the VAG-com apart from the oxygen sensor heating element beginning to fail and he even said my car feels like a chipped S3 should.
Coil packs were changed. Car is 2001 and only has 52,000 miles.
Maybe I'm imagining things but the car certainly seemed to boost quicker before this odd noise came about.