I'm happy to have just found this forum as my AEG-74600 started to emit this rattling sort of sound when pumping the water out. After a while it stopped and a "C2" message showed up in the LED display. Apparently this indicates a fault with the pump:
So I did an emergency draining by with the emergency emptying hose followed by unscrewing the drain pump cover. I discovered that the green "propeller" or "fan" if you like was completely loose, and my first thought is that this is the cause of my problems. I assume its job is to "push" the water through that area and out, and being loose it probably won't pump the water out properly.
Anyway, I guessed it was broken off, but upon closer inspection it appears just to have loosened but I can't seem to just screw it in place (the pump just spindle just moves if I try). Is there a special way to do this?