I have bhk 300 monos, dsd, bhk preamp and a p20. When I bring the bhk preamp out of standby it also triggers the amps to turn on. About 10 seconds after the amps come out of standby, I hear a light whistling / wish sound. This just started a couple weeks ago. Anyone have any ideas what could be causing this. The sound last for about six to seven seconds. I also noticed that when I’m not playing any music if I put my ear up to the right speaker I hear a light put put put sound. It’s not audible from my list ending position which about 12 feet away but I can hear this initial whistling sound.
My first thoughts were the tubes. The bhk 300 monos are on their stock tubes and they are just over a year old. I replaced the tubes in the preamp and they have 1051 hours on them.