bosch dishwasher SGS4012GB/07 humming on wash?

i have the bosch SGS4012GB/07 diswasher i have had it about 12 years and the only thing that has gone wrong was the door seal this was replaced about 2 years ago. it has now devoloped a very strange hum while washing, its quite a loud hum but at the same time quite low (a bit like the base on my sub in the lounge) does anyone have any ideas what this could be, im dreading it being the main circ pump as i cant afford a new one just yet lol

uksausage dave
July 2010