The clutch in my 1983 Chevy truck rattles when I push it in

Could be the release bearing is bad or you could have bearing noise from tranny

Its the thrust bearing inside the gear box. its a cheap part but you will have to take the gearbox off to do it.

the thrust bearing pushes up against the clutch when you depress the pedal, its a bearing type part with ball bearings around a plastic and metal shell, at worst these can come free and damage the gearbox.

US may call it something else but the part in the UK is a thrust bearing.

hope this helps

The thrust (release) bearing is worn, not a big deal in itself as it will last a long time like this, but if the noise annoys you the bearing is very cheap, though to change it means removing or pulling back the gearbox so if the clutch is not new you could replace the whole lot as easily while in there