Aftermarket intakes introduce a ton of turbo noise which often sounds like flutter but is normal. The stock turbo inlet pipe also adds to it, when I swapped mine out to a larger one a good amount of the flutter sound when lifting off throttle went away. I'm assuming it's just due to resonance on the smaller inlet.
I'd bet 99% chance that it's just normal noises from the turbo but if you really wanna be sure you can unplug the DV and then listen. Obviously, if it sounds the same you got a DV issue but it's a pretty rare failure.
PS. While I wouldn't recommend running a disconnected DV full time a few small pulls to listen while disconnected won't do anything besides a check engine light. Lifting under partial boost will make the most pronounced noise.
I ran my IS20 with the DV disconnected before I swapped it out for about a month because I loved how it sounded like a big turbo supra. When I pulled the turbo 0 shaft play and it was in perfect shape. I even had the plug on the DV on my is38+ come loose on the track and I didn't notice till it threw a code an hour later on the drive home.
Also, learn from my mistake an aftermarket DV is nothing but headaches.
