bosch dishwasher making odd noise

I haven't used salt for a month or so as use 3 in 1. The dishwasher is making crackling noises from low down. Noise disappears when water fills up dishwasher, then returns.

Is this a limescale problem? If so, what can I do??

Is it something else????

Thanks
Lydia

something stuck in the pump .

Whatever your crackling is,you must use salt in a hard water area.
These 3 in 1 tablets can't flush your regeneration unit.

look at the heating element in the bottom. Is it covered in white or grey scale? If so start using salt again. Look at your instructions to see how to adjust the dosage to a level that will keep it clean. A scaly element is the sign that you need salt. The scale will crack during the drying cycle. The 3 in 1 tablets are not good enough, you get better results using a simple tablet plus rinse-aid plus salt (cheaper too)

On my d/wr, the element is bright and shiny like new (but I have a whole-house softener)