More detail with this question(than the other thread), it sounds as though the pump could have sucked some crap up from out the tank, especially if run low.
I believe these are external pumps ?, if so you can take the wires off, and with a battery pack or similar reverse the power to the pump, this often dislodges any crap in there as it then flows backwards, but if this works of course it means the tank needs cleaning out.
Reversing it will do no harm, for about 10 seconds at a time, you will actually normally hear the bits of crap getting booted out.
tabetha