My audi sport muffler whistles or howls when I really punch it, high rpm's. The Dealer said it would go away with the carbon build up, but 15,000 miles later it has just lessened slightly.
My only upgrades are K&N oil & air, a 240hp TT bi-pass valve, and the audi sport muffler.
Any thoughts?

 

My S4 let out a howl the other day, on hard acceleration i was concerned it was from the engine bay but my mate reckoned it was from the rear, thanks you may of answered my question i last posted. rob.

 

Are you sure it's your muffler?

 

that howling sound makes me think turbo

 

It is definately coming from the exhaust/mufffler. Since my last post I totaled my 2000 and got a 2001 and it has happened on both, and only with the audi sport mufffler on, not the the stock ones. A independent audi service guy looked at it and agreed.