My other car is a MINI!!!!
your DV is in backwards mate, if you're running high boost on a standard spring, it will be forced open for sure. Flip it round to the side of the DV goes into the throttle body hose.
Also, I don't like the look of the vacuum line, have you used a joiner to connect into the old DV top line? It gives you WAY too much un-needed hose and much more chance for a leak. If there's a leak in that vacuum line the DV won't be opening as it should at all, and also won't be held shut under boost, so with it being in backwards, you're probably loosing boost!
Trace the original DV feed back to the inlet manifold (may be the FPR on some) and plug the silicon in there directly.
The noise with the cold side kit is definately different though, dont worry about that