Probably because it's a GE!! lol
Seriously it might be because one of the tub counterbalance weights has slipped. Had that happen once and it made a devil of a racket!
We had that same model and it made a racket! Not only did it have the usual GE transmission roar, but in the middle of the agitation their would be a loud rhythmic "squawk" in time with the agitation strokes. With what I know now I'll bet it was an engineering defect inside the agitator spline where the metal was slipping on the plastic. This machine retro-fitted with a spiral ramp activator would be a winner. If it is exactly the same model as ours(and it looks to be)it will have timed bleach and fabric softener dispensers in the lid well with an accessory dry detergent dispenser that sits on top of the super filter-flo pan. Good luck! and if you don't want it, I will.
These always catch my interest. Nothing like an avocado GE with a lighted control panel. Is this one from around 1970ish or so? I need one of these for parts!