I drove down to coast 3 weeks ago from Johannesburg (1600m above sea level). I have a downpipe, Forge Intake, Forge DV on my 8P S3. The car obviously got louder as I approached Durban ( coast - due to the denser air). I did 1500 km in Durban itself during the week, doing mainly highway driving. Anyway, after driving about 900-1000 km at the coast, the exhaust had changed dramatically. The car became quiet quiet quiet. It actually became softer than stock. The normal raspy noise had dissappeared. I logged the car, and all was perfect, boost, timing, ... The airflow was actually the best I have ever got. I drove back to Jhb from Dbn, and the car is even quieter in Jhb (obviously, with the air being thinner). I can actually here the turbo spooling now.
I am confused now !!! What do you think could have changed my exhaust note from a nice raspy D/P sound to very quiet ???? I can not work it out. The only variable that changed during the time the sound changed while I was at the coast, was that I ran a small bit of octane booster in half a tank.
At high rpm now, I pretty much only here the turbo spinning. Even if I open the windows to hear the car, the turbo noise has increased as compared to the way the car sounded previously.