air pump and ugf questions

i've had a 40ish gallon (22 x 36 x 12) tank for some years now. it has
an under gravel filter powered by three tubes with air stones in them.
its in the living room and the pump noise bothers me from time to time.
i'd be interested in noise reduction techniques for a tank in a high
traffic area like the living room. however i have some details which
may show that the noise is my fault. when this was originally set up
money was tight and i had various pieces from older aqauriums around,
as a result this is how its set up today.

1 maxima dual feed air pump (i cant find a model number but all maximas
seem to be rated at 30 gallons.) both feeds connected to a air tee
then a single hose going through a check valve and then up to the very
high tank top where its pushed through a 4 way tee/valve set to
distribute to the 3 air stones. yes i know its a hack but it seems
to have worked well enough. however i am starting to wonder if my pump
is louder than it would be if i had a more normal setup/larger pump.
i would be all for a larger pump assuming it doesnt end up being
louder. so anyway i know that the check valve can reduce the air flow,
does this make the pump louder? if so i can probably figure out a way
to get it up above the tank if i had to. i have also read that having
an open valve bleeding a little bit into the room can help reduce noise
that might be cause d by back pressure. i must also admit to not
repalcing the air filter in the pump for who knows how long and to not
replacing the air stones often enough. so comments/mocking/advice
would be appreciated as to what the best setup would be for noise
levels as well as fish health.

one last question. the ugf i have is a basic model that came with 3
carbon filters that top the rise tubes. once again i probabaly dont
change them enough. i have read that they will do very little good
unless changed very frequently and even then the filtration they
provide is almost usless, on the other hand they can arrest water flow
up the lift tubes as well as actually release conaminents if not
changed regularly. comments? should the filter tops be removed?

note: right now the tank has plants and is home to 3 roughly 2'' fish.

thanks for any replys