Does anyone else have this problem with the Ashdown Superfly head? Basically, a few minutes after switching it on, it develops a high pitch whistling sound. This is at a constant volume, irrespective of the volume or the eq. Indeed, it doesn't go away or decrease with the volume at zero and all the eq parameters turned right down. This is a separate sound to the idle hiss most amps have. I did take it back to the shop but the guy who sold it to me seemed to think this was normal. I think the problem was I didn't leave it on for long enough for the noise to get to really irritating levels. It really is noticeable.
Has anyone else had a similar problem? Any suggestions on what I should do?
Thanks in advance,
Nick.