A GM engineer proves the unlikely to be true: Click and Clack are sometimes correct!
I read your column recently about a 1990 Buick LeSabre that had an occasional noise sounding like an open muffler when driven in the rain. I am an engineering manager with the Flint Engineering Division of General Motors and am familiar with this problem. The noise occurs when the exhaust pipe contacts the intermediate heat shield, which is located between the exhaust pipe and the floor pan. The touch condition can occur when water is splashed onto the underside of the exhaust pipe. The rapid cooling and resultant contraction may cause the pipe to bow upwards making contact with the shield above it. The noise will stop as soon as the exhaust pipe returns to normal operating temperature. There is a dealer service bulletin on this situation that can provide the dealer with the appropriate, permanent fix.
RAY: Thanks a lot, Ron. Believe it or not, that was one of the possibilities we suggested to the guy with the LeSabre.
TOM: So you can imagine that it comes as quite a shock to us to find out we were actually right! Will wonders never cease?