Grinding sound disappears when clutch pressed down, what's wrong?

Because it is most troublesome with the clutch engaged (putting load on the gears) it sounds like the lube level is seriously low in the gearbox. You should have the gearbox lube changed - you don't want to keep the old, abused lube that is in there now. The gears won't last long without decent lubricant.

if it were the clutch it would happen when you pressed the pedal and the trans when you release the pedal and hopefully you are just a bit low on the gear box level but if you keep driving it will keep making the cost to fix rise

since the clutch tends to be one piece when you release the pedal (no moving parts) I am sure its the trans

this is typical of thrust bearing wear to replace this it is easier to replace the full clutch kit as the release (thrust )bearing is a part of the kit up to £100 for this and maybe £200 to fit ring round your local garages and ask them for a price on this as the only way to do this job is to seperate the gearbox from the engine you can DIY this but only for the experienced home mechanic

i would say you need a new clutch and/or gearbox the noises made are quite possibly a sign of worn out or mis aligned parts this is not normal and need seeing to as soon as possible or you could end up with a hefty bill for repairs

it,s the throwout bearing. for 1 thing the throwout bearing is only suppose to run when you push the clutch in.

Clutch is shot. Might cost more to fix than it's worth.

you may need motor mounts.