Hey guys, so I recently started noticing a flutter sound from my engine bay. It only happens during throttle lift at low boost levels, like around 1-8 psi. I've researched a ton and everyone is giving mixed info on what it could be. I didn't think it could be the waste gate since it doesn't occur under load and building up on boost. It only happens when I lift off the throttle. I tried a couple steady 3rd gear pulls all the way to 11psi and I get the the o'so good "pssshh" sound when I lift off, but at lower boost levels I get the flutter.
What I've done prior to hearing it: defi boost gauge install, and the solo instruction event. I also have to confess that I had a k&n typhoon sri without a tune during that event

(dumb move I know, but it's been on the car ever since I bought it) but I'm getting a stage 2 flash next week from kspeed I promise. But anyways, any ideas on what the sound could be? Stock BPV maybe?