Very loud noise from transmission

My '94 V8 Auto has developed a VERY loud vibrating/buzzing noise which seems to be coming from the transmission/diffs. It is OK when idling or if the engine is revved in neutral but when in gear, as soon as it gets above about 1500rpm it gets louder and louder and 50mph+ it is almost deafening.

The car seems to shift through the gears OK and kickdown still works, but obviously the noise is of huge concern, particularly given my recent woes with a sudden loss of transmission fluid

I am expecting my worst fears to be confirmed... that this recent problem has knackered the autobox and the signs have taken a few weeks to appear. Also, the noise stops as soon as take my foot off the accelerator.

Any ideas (other than to get it to the garage sharpish)?

Turns out it was the rubber coupling on the prop shaft, which was well and truly knackered. Lucky escape. Fingers crossed that's it for expenditure for now.... MOT coming up in November though...

phew!