Why is my washing machine making this sound?
Likely a failed transmission (I was going to go with bearing before I heard the video) and likely costs more to fix than getting a new washer (almost certainly costs more to fix than getting a clean, working used washer.) But, if you like to look, look up the "tricks" to getting into your model of washer (the last one I tore down had "places you shoved a putty-knife" that unlatched the cover) - there's usually something non-obvious like that, but the internet has largely circumvented these "trade secrets of the appliance repair trade" if you look hard enough.

It's also helpful to look for "common problems" or just problems and your model number.