Grinding noise when letting off accelerator

Hi

I have a mk1 golf campaign and just tonight when driving home I noticed what sounds like a grinding noise when letting off from the accelerator, what could this be? It sounds like its coming from the back but Ive googled this and it could be gearbox problems.
Any advice?

Cheers

Andy

i would jack the back up first and check both wheels for wheel bearing/drum brake issues also check the hanbrake cables dont touch the wheels

I forgot to mention it does this at standstill when reving so don't think they would be making noise unless I was moving would they?

Thanks for the reply

Andy

Will it go away if you push the clutch pedal in?

Ive not tried that ill test tonight, it does it everytime I let off and is louder the more revs I put on and sounds quite metallic. Could it be my exhaust?