Hello

I changed the Transmission mount myself, by supporting the Transmission and removing the Supporting Crossmember, in the driveway. I did not remove the Drive Shaft. If it sounds like a truck, then maybe your exhaust was disconnected at the flange, just below the Manifold, or the bolts were not replaced, or the Nuts have come off or not tightened, or the Exhaust is cracked. I did not have to remove my exhaust, but maybe the mechanic did. Just below the Exhaust Manifold, attached to the Front of the Bell Housing, there is a Exhaust Suspension "system". Earlier cars, it was a Bracket, later cars, it was a Spring. Many, many, many Mechanics remove this and do not replace it and I have been told by them that do "It is not necessary." Just after I bought my first Volvo, I had it serviced. The Mechanic removed mine, for whatever reason. After that, I began working on my Volvo, as I learned more about the car. But, I had to continually had to tighten the Exhaust Flange Nuts, until I replaced the Bracket. The Exhaust System can only travel so far upward, because of the bracket or what remains of it. May I suggest you lie on your back, just behind the right front tire and look up at the Exhaust, with glasses or Goggles because lots of road debris will likely get into your eyes. Grab ahold of a Cold Exhaust and try to shove it around, up and down, to notice where and why it is making contact with the underbody. Get a mirror and light to inspect for Exhaust Leaks and Cracks -Full Length, looking for Cracks with Black Sooty Traces or Rusty Holes.