A silent UPS

[Da Rock]

This may sound like a strange question, but is there a way to mute the
voice box of a UPS? I have a highly specialised application for one- I
need a mobile desktop pc (very cheap). I need to setup a pc for my
little girl so that she has music, video, and visualisations while she's
in her cot- which is mobile and moved from room to room. So I don't want
to shutdown the pc when in transit, and I certainly don't want any
shrieks when I unplug the power...