86 jimmy 4wd- trans question

when in neutral and you release the clutch, there is a vibration and grinding/scraping sound coming from tranny. Clutch doesn't slip. Any ideas as to what the deal is. Thanks.

Being an 86 the mainshaft bearing comes to mind.Could also be the throw out,for some odd issue,but if you shove the clutch in and the noise insatantly stops I would put money on throwout or something close by.If it takes anytime at all to slow down or even changes i'd bet the mainshaft.