A/C noise


I recently aquired a levinson 38 and upon powering it up I can hear a/c noise which is not prevalent in my other pre-amps...my question is: 1.is this normal for this make/model 2.is this a ground loop problem or 3. does it have a bad cap? It is on a dedicated circuit but is running through a monster hts5100.Thanks.
barrett
900 feet???!!! It sounds like an old adcom amp when powered up...slow hummmm 3-4 feet away. I cannot detect it when music is being played but I know it's there.