I had a similar experience as OP. I removed my house batteries, leaving the coach battery in, for a repair on the battery rack. After the batteries were removed I kept hearing a relay clicking a few times a minute. It was coming from the battery control center box next to my inverter. I had already thrown the battery disconnect for both coach and house. I went ahead and threw the inverter/converter physical disconnect switch (which breaks that circuit) and then it stopped. It makes sense, but I bet on most coaches (like mine) the circuit that contains the inverter, BCC and batteries are not separated by the battery disconnect switches, the battery disconnect switches just separate this circuit from the other load components (if I said that in a way that makes any sense).
So back to the OPs situation, I guess +1 for dpinvidic's point about the solar panel