I'm with others that think you should wait on replacing the ATS. I have the ATS attached to the back of the AC breaker and 12V fuse panel in an upper cabinet in my rig. If you can hear it buzzing near the breakers, it might be like mine and inside it's own metal box attached to the back of the breaker/fuse box.
Now, a couple other things...the ATS could just need a good contact cleaning, or the shore power may be weird in some way (but your surge guard would have disconnected you from shore power if that was the case), and then you might have something going on that's fairly common...low batteries.
If your converter is drawing a lot of current to charge up a very low battery, you can sometimes hear a noise from the ATS, even though the Converter itself is relatively quiet. (Ask me how I know). A bad battery, or an undercharged battery can draw excess current while charging, but it's not enough to blow a breaker on the converter sometimes.
Check water levels in the batteries, top or if OK, let it charge up for several hours and see if the buzzing goes away.
