Try a different plug. If you turn something on amp ur amp pops is probably on the same circuit and apartments are wired by the lowest bidder I have personally seen some interesting wiring jobs in buildings like that.

But it might not due any good, since all the units are likely grounded on the same block.

Option 1 :shady cheap method:

Go to ur local hardware store for about a buck buy a plug that turns 3 prongs into 2 ( this isolates the ground which is were U usually pick up noise) U can then run a ground wire from the little metal clip on the plug to any ground. (this is not necessary but in case ur building gets struck by lighting or something it will be safer)

Option 2 Expensive:

Buy a quality power condition which will be more money then your amp.

I would try option 1 I use it a lot to kill 60 hz noise in various electronics