Michael Dauria wrote:

I live in an apartment. The apartment has natural gas appliances. The
natural gas furnace lives in a little locked closet above the stairway
going up to the second floor. I am pretty sure the natural gas water
heater is in there too (I hear a loud click every once and awhile that I
assume is the water heater).

Now for the strange part. When I am in my bedroom at night I sometimes
hear a strange noise. This noise happens randomly (although last night
it seemed more frequent) in 5-10 second intervals. It sounds like
pressure is being released (it sounds like when you let air out of a
ballon with that whiny sort of noise).
SNIP

My prime suspect would be the water heater.

The fact that it happens (only?) late at night
could mean that city water pressure jumps up then.

Find out from maintenance where the heater discharges
to when the relief valve opens. Might be to an indoor
drain or even to the outside. Monitor that for signs
of water being discharged. If it *is*, you have some
leverage to work with.

Jim