The past 2 times we've camped (we had electrical hook-up both times), upon connecting power to our TT, my family noted a very high pitch tone coming from the breaker panel. It wasn't loud, but loud enough that we all could hear it and annoy us. I flipped the main breaker off in the TT panel and it stopped. When I flipped the breaker back on, the tone came back. After a few minutes of putting up with this noise, it stopped and never came back for the remainder of our camping trip. At the time this happened, no accessories (microwave, A/C) were on.
What I described above happened both times we camped.
I did have the following Surge / Voltage Protector connected:
Any thoughts on what might be causing this?