Hotpoint FDL570 rumbling noise

My dishwasher has started making a loud rumbling noise and dishes aren’t washing properly. No error lights come on – any cycle I select completes. I’ve checked the filters and arms and they are all clean, except the arms don’t seem to have the same power as previously. If I purposely put a tall item in the lower tray the arm rotates and stops at it instead of clunking past. Water fills ok, heats and drains.

I’m guessing the pump is the problem, but is there anything I should be checking that may be causing this problem before writing it off as an expensive mechanical problem?

Thanks.