I've stayed in POR-AB twice, mansions, once..Polynesian once, BWV a bunch of times, AllStarMusic once, POP three times, BCV once, CR once S/D each once. I have to say, the noisiest stay I had was at the Polynesian. We had a room with a connecting door and we heard everything from next door. It was awful. The nights were bad because kids insisted on running down the halls, hitting each door as they went and then again in the morning!!! My stays at POP were all incredibly quiet...I never heard a peep from my neighbors. Same at Music. POR, all rooms, were really quiet. The one time we had a connecting room we were there with another family and they were in that connecting room, so it wasn't an issue.
I think all the resort rooms are pretty quiet. It all depends on what the neighbors are like. Flushing toilets don't bother me...I hear them at my own house, so I"m not going to complain about it at WDW.
If you're close to an elevator, then you are going to have to expect more noise...comings and goings as well as elevator noises. But, that isn't an issue at POR-AB. For those bldgs, I love the further out bldgs, way at the back.