I have a strange situation where I hear a constant background noise whenever I first power up my amp and take it out of Standby mode. The noise is a combination of a faint, high pitched squeal and a swirling, whooshing sound, like white noise and radio static with some movement to them. However, if I briefly unplug the instrument cable to the amp's input and plug it back in, the noise stops and doesn’t come back ... until the next time I power things up from cold. Basically, the noises show up whenever I first power up the amp from cold, and either: With the instrument cable already plugged in when the amp is first powered on. With the instrument cable plugged in after the amp has warmed up. In both cases above, this is before I flip it from Standby to On. To clarify further, moving backwards from the amp input jack to the guitar: The instrument cable from the amp is plugged into a passive TRS passthrough module on my Emerson pedal board. It is then connected to a series of pedals, all powered by Strymon Zuma power supplies. The Zuma power supplies are plugged in to an Emerson power module, which has an IEC cable to my voltage regulator/power conditioner and wall outlet. From the tuner input is an instrument cable connected to my guitar of choice. The two instrument cables, from the amp to pedalboard, and pedalboard to guitar, are 10' Runway Audio cables. It is nice that there’s a simple workaround, but I’m curious if anyone has an idea what the root cause might be, or if it signifies anything serious in need of addressing?