High pitch noise after throttle let off

[E_KEL95]

Cars developed this noise happens after you let off the throttle and the revs drop to near idle..have a video of it ill upload
Note in video it's the 2 high pitch noises at the end of each rev, sounds like it's coming from The round bit with the pipe coming out of it just in front of the egr pipe? Any help much appreciated and is it serious/expensive fix?

http://s1271.photobucket.com/user/205-G ... r.mp4.html