Loud Humming Noise
You're describing vague, conflicting information. At first glance, I would think you have something stuck in the pump. But then it would be there in the rinse-only cycle also.
The anti-bacterial mode heats the water up to about 180F. This kills bacteria, and it also speeds up the action of the detergent. It could be dissolving whatever is in there.
The humming noise wasn't there in the rinse mode... The heater isn't on in the rinse mode - everything else is. But I've NEVER heard a heating element hum.
Cleaning the filter:
The filter is in the back in the bottom right. It's cover is held on by two 1/4 in screws. Under that is a large grate, and I sometimes find stuff clogging the screen (underwater, toward the center of the machine.) I'd start by looking there.