I have the same issue but if I turn on an extra light around the camper it'll go away. It's annoying but I don't think I can recreate the random high pitch noise if I took it into the dealer to fix.
I had the same problem and dealer couldn't replicate. So the next time we were out, I recorded a video with my phone of the noise coming from the converter box. I emailed it to them and they ordered me a new box under warranty. They replaced when it came in and I haven't had a problem since.
'16 Ram 3500 MC CTD Dually, 4:10 rear
'14 Ram 2500 MC CTD (gone)
'14 287BHBE (gone)
'16 North Point 377RLBH (current and hopefully last)