Richard, welcome.
It should make a whirring sound - grinding, thumps and bumps aren't good. Look for something loose that's slopping back and forth excessively. If you can't see where it's moving, have someone else turn it while you listen. If you still can't pinpoint the spot, hold your hand on various parts while it turns. Eventually you'll find where the bump originates. Good luck. Let us know what you find.