So I have been doing some research on the forums to see if anyone has had this problem. It seems people have (thread title Fluttering Sound Under Hard Acceleration) but I have yet to find a definitive answer.

When I am accelerating in the 3.5-5.5k range through gears 2-5 I hear a flutter that interrupts the spooling sound of the turbo. It goes away at higher RPM. The car doesn't buck when the flutter occurs. Mods are ETS intake and UICP along with a OTS Cobb 93 octane COBB SF LWG map. The sound was present before the reflash (just installed 3 days ago). 08 GSR.

Any ideas????

 

I have the same problem, except mine bucks

 

Similar problems, my thread is a few below this one.

 

Partial throttle flutter. I think it's the mid way point between spooling like the bov is partially open to reduce surge. So basically step on it!