It's quite a simple job to whip it out and inspect it. If you have VCDS then often you'll see a fault code stored.
Stu, I'm not sure what you were "whipping out and inspecting," but I'll have to remember next time a youngster like yourself says it is a simple job, I should remember my age (and size!)
Well I thought I'd try anyway!!
It started badly for me when the wheel decided to be stubborn, and not come off as easily as it should, and I have had over 40 years of practice so it's not a new experience for me.
However, having managed that, I removed the inner wing lining, and then struggled for some time to remove the old DV. I do have some reasonable kit, including a socket set with cv joint type extensions. I couldn't get enough purchase with even my best alan keys to loosen the bolts, so without the socket set and attachments it would have been impossible. You do have to be a bit of a contortionist for sure.
At first it looked ok:
But then I looked closer
Though black marks around the diaphragm look like the beginnings of more splits too.
Anyway, after much cursing, and lots of skinned knuckles, I finally got it all back together and went for a test run.
is all I can say, it's so good to have my boost back.
So to the OP, if you can hear a whistle continuing after the whoosh when you ease of a bit from hard throttle, then your DV is probably shot.
TonyZ