How can I fix my CDA CW496 Dishwasher?

CDA CW496 Dishwasher makes deep bubbling / rumbling sound part way through cycle. First time it happened, the cups etc were not clean at the end of the wash and the double feeder arm which supplies the upper spray arm had been pushed upwards out of the holes next to the lower spray arm. I pushed it back in and next time was ok, but since then I have had to push on this plastic feeder whenever it makes the noise and all is ok. However, today, that has not cured it and the noise continues. Any ideas?