I'm getting a faint buzzing sound from my Yamaha CA400. I'm at a loss to work out why, so I'm hoping that from my description of the symptoms, someone might be able pinpoint the cause.

The buzzing is audible when the volume control is anywhere between the nine o'clock and three o'clock positions - it disappears outside this range. Apart from this, the volume of the buzzing is the same regardless of the volume control position.

It's not loud enough to be distracting, but I could live without it if there is an easy solution. I'd be most grateful for any advice offered.