did your dealer scope your motor for carbon while it was there ?

The sound is normal but the problem is probably the BOV. Euro cars ECU is quite sensitive and not liking it when is venting out and prefer an enclosed system. I am sure Forge have a recirculate hose/part in the kit.

This doesn't seem like a turbo issue to me. You should have disconnected your turbo inlet pipe and looked at the turbo fins and inspected the shaft play, I think you'd know if the turbo going going on you. It also sounds like you don't like the sound of the forge DV/BOV, that's really common, in fact if you install a performance air filter on a stock car it is also very loud.

I'm having a similar issue, however like Preme123, this goes away if you provide some gas upon start up, or by turning the caR off and on after warm up. To me it sounds like an idle issue, but my car keeps throwing a cam shaft positioning code. Not sure what I thing, on my old VW I could adjust the idle, and I'm interested to see if that would fix this problem.

Just to update, I also once had the camshaft angle offset code regularly as well as misfiring codes. However, after I replaced the engine mount, transmission mount, new spark plugs, new hi-pressure fuel pump, and new fuel pump in the back/tank?.

Now, I'm trouble free, no more codes! Hope this helps.

There are 2 forge BOVs for our car. An atmospheric valve which dumps the air out, and makes the sound everyone loves and the recirc valve which is what our car prefers. Sounds like you got the first one.