Does it go away if you put your foot on the clutch? If so could be clutch release bearing.
Maybe start of Syncromesh wear? Without hearing the noise difficult to say, but mine does make a noise that I would describe as you have, and I know the Syncro is going.
Always worth a look at the propshaft UJs, they frequently produce metallic noises when about to give up.
I had what sounded like similar noise which would happen when slowing down coming to a stop, in my case in the end it was bearings in the LT77 gearbox shot so had to fit a recon. When i got it out though the bronze spiggot bearing in the end of the crankshaft was also knackered I am told these can make strange noises when loose. Have you checked / changed gearbox oil. I fitted the recon gearbox a few weeks ago and since then I have now become obsessed with noises and rattles like it some kind of disease. I had a bad rattle in time with the engine when driving which made me think I had problems with the transfer box but figured it out today when I put the storage box in between the 2 seats a longer bolt was touching the top of the handbrake cable was all it was.
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