Hoover top loader 600MB. When spinning on fast speed the drum is hitting against the machines body. It is like it's off balance. Hitting from side to side....and noise.

SOURCE: drum off balance

It's either a bad suspension spring or you have a crack in the tub support.

SOURCE: Loud banging noise durning washing machine spin cycles.

First plug off the wall. Open the machine from behind to examine if any shock-absorbers(known as dampers) or springs have come off or broken. Your dealer could help with spares. But you could do the job yourself.

For spares:
RepairClinic.com (which is good)
espares.co.uk
AppliancePartsPros.com

SOURCE: top loader hoover 600mb automatic washing machine

If this machine has a motor that uses brushes, check them for damage, wear, or weak/distorted springs.

SOURCE: washing machine is off balance

Not fixed but it still goes so I guess i'll just keep using it till it breaks down altogether

SOURCE: Hoover 600MB Top Loader, Won't Spin

I have the same problem. Just started missing the spin cycles and now I need to find which part to replace.
So far I think it could be: Aged contacts in the Timer, a faulty spin/no spin switch, or something to do with the brake/release mechanisms etc. ..I do know that the problem is electrical because everytime the motor starts the spin works fine; therefore eliminating in my opinion, the mechanical gearbox bits as a cause.