Buzzing? You don't say if it has the 2 speed rear end. My 57 GMC Bigbolt has a geared adapter that is screwed onto the speedometer, then the cable screws onto it. There is a post with a wire that comes from the 2- speed shifter switch. This adapter keeps the speedometer correct, when in either hi or low, rear gears.
Your buzzing may be coming from this adapter. Mine had so much old grease in it, that it was hard to turn. I think that may be why the speedo cable was broken when I got the truck.
Anyway, I cleaned mine good and lubed with a light weight oil, installed a new cable and now all works smooth and fine.
