1993 Volvo 850 2.0 20 valve saloon manual

When I purchased the car 7 years ago I complained to the main dealer who sold me the vehicle that there was a noise during acceleration; usually heard when pulling from below about 2000 revs. The car had about 23,000 miles on the clock.
The dealer said it was due to a vibrating heat shield over the exhaust and I believed him.
The car has now covered some 107,000 miles.
The noise has become louder to the extent that I would probably find difficulty selling the car.
It sound like a noise from the transmission; I don't think it is the heat shield.
Can anyone suggest a possible reason for this noise?
The car has never given me any trouble and has always performed well.

 

I had such a noise. 93 240 wagon at 70K(now 110K). Removing a part of the
heat shield fixed it.
How are you sure it is not the heat shield? If the car shifts smoothly and
the engine runs well, then they are unlikely sources of trouble. Sheet
metal can make a lot of noise when vibrating and touching something.

sold me the vehicle that there was a noise during acceleration; usually
heard when pulling from below about 2000 revs. The car had about 23,000
miles on the clock.