[s-cars] Whistling

[Andrew B]

I've got a faint whistling noise coming from the passenger's side of
the engine bay at idle.  Just a pretty constant whistling noise, not
too worrysome.  When I rev it a little, you can hear the noise go away
and switch to a wastegate/turbo sound, but when it's released it goes
back to whistling again.  I recently had a buttload of work done to
the head, but I didn't notice it beforehand.  I didn't spend a lot of
time under the hood before it was repaired though.

What gives?  Sound normal?  Something to keep an eye on?  Oh my God
your car is screwed?

-Andrew