Vibration/noise

My 94 SC2 DOHC 130K miles is starting to make low frequency noise and
vibration. After sitting overnite (cold) , after starting and putting gear
in reverse an odd rumble/growl/vibration occurs when idling stopped. If I
let off brake and start rolling in reverse it ceases until I stop again.
After a few minutes of running the majority of this noise will clear out.
This has been happening for a couple of weeks now. Also now the foward
gear is making this low rumble noise especially at highway speeds. 6
months ago I replaced the upper T axis mount because the steering wheel at
idle vibrated so bad I couldn't stand it any more. The new mount made it
seem like a new car. I'm wondering if the lower mount or the transaxle
mounts could be bad. Has any one had these replaced --how many miles?

Is this something a shade tree mechanic (me) can tackle with limit tools
and skill?

The tranny shifts and functions OK but if I let this continue driveline
components might be damaged?

Fluid was changed 15K miles ago and levels are OK.

Any help much appreciated.

Thanks.