ISTR that rabbits can hear high frequency sound inaudible to humans. A
fan that sounds quiet to you might be intolerable to the bunnies. I
suppose you'd only know if they showed signs of distress.

High frequency sounds are also most easily attenuated, which is why
you can only hear the boom, boom, boom of the bass drum when the
neighbours have a 2 am garden party.

Yeah they have occilating fans at the mo but these don't seem to
bother them at all. They are more than happy to lie there in front of
them when they are free to go outside if it was causing them distress.
It was more the volume of the air con that was concerning me.