Alarming rattle in gears 1-3 when accelerating

I have a D90 td5 and it started to make a high pitch squeal a bit like a belt slipping. About 10-20 mins later this squeal turned into a very loud metallic rattle (bag of spanners clattering around). I am guessing this squeal and then rattle is a bearing going somewhere. Would appreciate guidance on where this maybe coming from. Gearbox seems a prime suspect.

The noise was only present in gears 1-3 when accelerating and went away entirely in 4th. It also went away in neutral when revving the engine.

No problem with power from the engine, engaging / disengaging clutch or selecting gears.

Thanks in advance for any thoughts / advice.

Might be an idea to drain the gearbox oil and see if there are any bits of metal in it. Maybe transfer box too.

Col

Ok, thanks. Suspecting the gearbox slightly more than transfer box simply because the noise goes away in 4th.