I remember being told at some point that a horn sounds in one of the 744's gear wells if the IRU's are operating on DC power.
The ground crew call horn opetrates on most jet aircraft when the IRUs are operating and the cooling airflow is lost.
Many crews hear the horn, and turn off the IRUs. This is usually not necessary.
If the horn is sounding because the GPU has dropped off line, and you are starting the APU to restore ground power, then let the horn sound.
Depends on the aircraft but usually at OAT below 35degC, the IRU will happily run without cooling.
So many times I see crew turning off thr IRUs, then having to wait 10 mins to wind them up again, when there is no need for it.