Strange noise on boost above 4000rpm

[KiwiRS4]

Replaced the spark plugs over the weekend and noticed a new whistling sound above 4000rpm. It's definitely related to boost pressure but can't find out where the noise is coming from. Strapping a small child to the front of grill with the bonnet partially open to spot the noise is out of the question so it's onto RS246 for some advise.

I had to release two hoses off the y-pipe to get into the left bank. Thinking it was this I carefully checked everything ensuring no kinks but cannot pin point what it might be.

Any suggestions of where I should start looking?

[Blue_Thunder]

A pressure test would find it.

Possibly a loose spark plug?

[Virdee Autos]

Is the metal tube fitted snugly where you removed the rubber pipe from?

On mine the metal tube was just sitting on top off the silicone joiner, where someone had tightened it properly. The 10mm bolt was holding it, otherwise it may have popped off!