Last time I was at VIR I noticed that I was getting a very loud "thwacking" sound whenever I took a very fast left hand turn. Never happens on right turns, and never happens at slow speeds (>70mph). It sounded like somebody was hitting the side of the car with a rubber strap. My instructor and I carefully looked around the outside of the car and there were no obvious culprits. The one thing I did notice is that the heat shield over my exhaust has actually torn and cracked and there are marks on the exhaust tubing where the shield has either rubbed or hit it. Has anybody else noticed this, or does anybody have any ideas what the noise could be?

 

Check all of your exhaust hangers and such. check for play in the entire exhaust system. It could be your exhaust hitting the body/frame on hard turns.

EDIT: Other things to check:
All suspension bolts.
Bushings?
Sway bar End Links (I had this sound when I was autocrossing)
gas tank tight?

 

I'm almost positive it is exhaust related, especially because I'm fairly sure that the sound went up a couple decibel levels on my way home.

 

i would suggest adding some support mounts to the shield if it is moving or making sure the exhaust is secure if that is what is moving and hitting the shield.

the only other thing i could think of is a fender well shield, with larger tires often the clearances are close in the wheel wells, look at the plastic shields for any witness rubbing marks from the tires, you may have lost some securing clips causing the well gaurds to flap at high speeds and rub on the wheels.

 

Good idea, I'll check the fender well shields along with the suspension pieces previously suggested.

The worst thing about this is that its almost impossible to legally test whether I have fixed anything, lol.