Mines making a whistling noise too

I only noticed it when letting off the accelerator last night.
The more rev's when letting off the GO peddle the louder the whistle, that's about right though isn't it for a boost leak?
Yesterday I had the sticky vanes problem, put some Redex in and booted it a bit not had it again, hopefully won't have it again.
I'll have a look for loose pipes later.