I asked my mechanic about this the other day and he thought a boost leak could cause it. Can you remove or replace the BOV and see what happens?
Or maybe try a boost leak tester to check all the piping for leaks?
 
I had a mate once with a Ford TX3 turbo that had a very loud turbo. Like crazy loud whining sound. He had a tip broken off the compressor wheel. Yours looks fine though.