simple atnovido
Most APUs are noisier than GPUs. So if the work being done on the aircraft doesnt require the APU running. You can just use the GPU to provide electrical power for you aircraft network.
aside from that .. your APU cycles will get lower, saving your company more money and prolonging APU and its components life.
Another thing is that it depends where you work.
If line maintenance? You cant control the other carriers aircraft from making noise so not much help.
Its great that most of the carriers nowadays uses high bypass turbofans instead of those old banshee-like low bypass turbojets.
If base maintenance? You better ask the structures guys to work in a different shift? (just kidding) LOL
And if this is a personal opinion where you think aviation maintenance is just too much noise. I just have to say buy earplugs or ear muffs.