My 99 Lincoln 4x4 Navigator has recently started to make a vibrating noise when in drive or reverse and I come to a partial or complete stop. It stops when I raise the rpm a bit while holding the brakeor if I disengage and placein park. It happens in both drive and reverse. I got out one day to inspect and it seemed to either be coming from my exhaust pipe near the tranny as it slowed some when I placed pressure against the pipe. Baffling. I hope its not tranny but it does stop when placed in park. Any insight???