Anni- I doubt the loud humming noise is caused by your drain. Noises as described over the net are difficult to diagnose, but we hear this alot over the phone too. my best guess from SC is that the noise is caused when the toilet is filling up from the ballcock, and the type that usually makes the noise has a 1/4 brass arm attached to a float ball plastic or brass). these type ballcocks have a washer that will make a humming noise when the washer is loose or worn. it is possible to replace the washer if you know the model and manufacturer of the ballcock. geerally you get more bang for the buck by replacing the ballcock. Most home repair stores sell them for 5 bucks.