I've taken mine apart, main job is to remove all the torx head screws from the top, the rest just comes apart.
You might not notice once the top is removed but the motor section sort of slides out as a sleeve from it's holder, it is under this that you will see the cutters (macerator, like heavy duty cheese graters) that dice & slice the waste before it is pumped away, chances are something has jammed in this and it can't turn, hence the buzzing noise.
If you use a very large flat bladed screwdriver at the top of the motor/cutters you will know if it is turning freely or not, personally I connected the power (with the unit empty of water) to make sure they were spinning before putting it back together, but I can only say that I did this and do suggest for one second that you try it or that it is safe (or clean if it has any water in, as it will pump it straight out of the top at high pressure).
Make sure you don't lose the non return valves when you put it back together and that the rubber locating ring at the top of the motor is back in and seated properly in the lid.
It is smelly, VERY smelly, and no matter how much you clean the unit it will still stink, and so will you. Make sure you have lots of disposable cloths, a bucket, a bowl, and there is a lot of hot water in your shower for afterwards.
TheDr-UK
February 2011