If they're making lots of noise at
night, then almost certainly what you have are
flying squirrels. If I remember your general locality correctly, they'd be
Southern Flying Squirrels (Glaucomys volans). Flying squirrels are the only squirrels that are nocturnal. They're cute as all get-out, but might be inclined to gnaw on electrical wires.
I've helped evict them from people's attics before. If your landlord doesn't give satisfaction, you might try calling a local university and asking to talk with a mammalogist or an ecologist. (S)he might be able to give some good advice and/or be willing to come live-trap them and relocate them.
Cheers,
Michael