Ah, here's your post. I was going to suggest that maybe the board only takes a certain kind of file. Usually they take mp3 if sound is allowed, but who knows.

I've heard signals, like marker generators, and one of my laptop power bricks does that to nearby radios, if you tune across the dial there are infinite signal carriers, evenly spaced. I think when you turn the laptop off it warbles too.

Boomer