The APU is only loud if you are standing directly beneath it, otherwise, it's bearable to work anywhere around the aircraft without ear plugs. It is possible that you could be mistaking the sound of the air conditioning packs for the sound of the APU. The AC
packs are located on each side of the aircraft near the forward wing root. The high pitch noise is piercing, so it is typical to only use the right pack while the main cabin door is open. The left pack, of which 75% of its air goes to the cockpit, is usually turned on after the engines are started. While they are noisy, one can't complain of their effectiveness. They'll actually blow snow into the cabin even when the outside air temperature is above 100 degrees!