Drive Train Noise

[TransitNut]

I think I've now read most of the threads on this forum and haven't been able to locate one relating to this specific issue so here goes.
My 97 LWB 2.5Di has a rather annoying problem.
In 3rd gear at anything between 1,000 and 2,500 rpm the drive train seemingly "rattles". I say rattles as this best described the noise however there is no obvious associated vibration. It is not affected by how much the van is loaded (other than the "rattle" lasts longer when loaded as it accelerates slower).
It doesn't occur in any other gear at the same revs so it appears to be related to road speed and therefore I believe it must be related to the diff, propshaft or gearbox output shaft.
I will be investigating further next week but wondered if anyone had experienced a similar problem and could perhaps save me some time in identifying the problem.
I accept the motor is lugging a bit a 1,000 rpm but in 4th and 5th at the same revs it doesn't make the noise.

Cheers

[MrMPuk]

Does the noise stop when you take your foot off the throttle?

[gazza]

mine has done same for about 20000 miles now, no obvious faults with clutch or output bearing (new), prop or diff, turning the radio up seams to cure it tho

[TransitNut]

The noise only occurs whils accelerating.

[WINDSCREENGUY]

have you got underneath the van when idleling? anything loose like the exhaust that bolts to the cross member????