Hi George,
Air pumps should always be located above the water
level, if you locate it below the tank and it looses power for
whatever reason it is quite likely that water will siphon back down to
the pump, water on the floor and a short circuit when the power returns
with the potential for a fire.
Noise !! place a thin sheet of foam or an old mouse
pad under the pump that usualy makes them more or less silent.
regards,
unclenorm.