1987 244
155,000 miles
Just replaced rear transmission mount after noticing it was done. It was the original square mount. I replaced it with a Swedish made mount. Before I changed the mount out (it was broken on the side that connect to the transmission) there was a random clunking sound on take off sometimes.

I changed the mount and now there’s a grinding noise once I get to around 30 and then it stays grinding as I come to a stop and also persists when I put in neutral. Reviving it will keep the noise around in neutral. I put back in drive and at times it goes away.

I drive back to my lot and can’t recreate the noise.

The driveshaft rubber mound and spring appear to be fine (mount isn’t torn or cracking, spring is in good shape and not distorted.

Might the "grinding" actually be some sort of trans or bell housing contact with the underside of the tunnel? The new mount may have raised things up significantly. Can you tell if the pitch of the noise rises and falls with vehicle speed, or engine speed? If it's a manual trans the lower shift lever part might be contacting the edge of the hole.
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Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (getting ever closer to road worthiness)

Fixed it

It was the exhaust. It was rotting away and the muffler fell off recently. It was rubbing near the rear trailing arm mount.