Cambridge CXA80 humming sound?

Hi, I have just found out my CXA80 is making a humming sound. I've isolated the unit (disconnected everything) and still getting the same issue. Tried different power leads and sockets but still getting the noise. I'm assuming it's the toroidal transformer as from what I understand it's common for them to hum but if I put my ear up against the top of the unit the sound is coming from the front with the transformer being in the middle. Hmm.

I can still just about hear it from 2-3 feet away, a gentle hum nothing too annoying and I would guess this is relatively normal, but my girlfriend can hear it from 10 feet away! She was the first to notice. I don't have the best hearing but a bit concerning if my girfriend can hear it from that far away. Either that or she has the hearing of a cat.

Do any other CXA80 owners here experience the same issue?

Is it anything to worry about if it's audible from 10ft away? Not that I can hear it from that distance but I don't want to end up with a smokey! I was wondering if something might be loose inside the amp and if it's something I can fix, like tightening the transformer.