Anybody had a lifter than would come and go, making noise, on warm up. The motor will make lifter like sounds between 1200 and 2500rpms, usually only decelerating, and typically when warming up, not stone cold, but not full operating temperature. Doesn't do it at all idling, can't repeat the sound for more than 10-15 seconds, hard to get it at all sitting still, I really only get it at light cruise. Might very well be an oddball exhaust leak. Any thoughts?