When I let off the throttle at 5100 rpm my 2005 350Z; the car sounds like the horn is being beep! This only occurs intermittently from a dead stop shifting from 1st gear into 2nd gear. I do have a NISMO CAI and a motordyne plemum spacer which has been checked for leaks.... with no air leaks in the pass. Their is no noticable loss of power.

I have not check the ground yet.

Any ideas?