It's normal for these machines.
I don't know why but most Hotpoints, particularly the ones from the 90's up to 2001 typically bang very loudly on spin. I'd think it's down to poor suspension design.
Our WM52 was quite horiffic for it, we were driven out of the kitchen almost every time it span! The drum would bang on the back panel of the machine, then the front when it swung back. This was just on distribute!
They're meant to have an out of balance sensor, but I found ours tended to cut in when it was balanced and let it spin when it wasn't!
I think it's just one of those things you have to learn to live with on these machines. All I can suggest is making sure it's perfectly level on the floor and washing full, evenly balanced loads.
Matt