Harmen/Kardon 695 speaker issue?

My Harmen/Kardon speakers are emitting a very odd sound. Its not crackling but instead a loud beeping noise that increases in frequency, then stops and does it again and again. It almost sounds like a siren. The speakers ARE NOT plugged into the computer in any way and it just started doing this totally at random when I turned it on one day. Any help to what this could be would be much appreciated.