One time our GM van squealed when in drive. I took it to a transmission shop. The mechanic came out to where I parked and listened to it. He walked all around the van, then put his boot on the exhaust pipe - and the squeel stopped! I would have been happy with a $100 visit to a transmission shop but there was no charge. I brought a dozen doughnuts for the guys, went home and adjusted the exhaust hangers to get rid of the squeal.
Might be worth crawling under and listening carefully to just where it clangs. A mechanic's stethoscope would be handy.
