I'd say it's the sound of the exhaust going through the wastegate, bypassing the turbo under boost.

Does the wastegate run through the mufflers also? (either way, it's gonna sound different bypassing the turbo)

Moss

 

yeah wastegate goes throught the muffler also. i think its both the turbo and wastegate making horrible music together. maybe tommorrow i can get a vid. being on watch at night and doing a turbo uninstall on a guys truck during the day take alot of my time. but it gives me a free meth kit and a free electronic boost controler.