Just updated all my neural devices to the latest FW (Quad Cortex/Nano Cortex). So far, this seems to have fixed my problem (halleluyah!!!).
Powered the Quad Cortex off and on multiple times in a row - no more noise upon bootup, tuner acting normal.
Now there is a new question:
They seemed to have replaced the Standby with a “be right back” mode wich seems to do the same thing (all audio off, screen goes to sleep) - When I was having the noise problems, at shows after soundcheck, I kept the device in standby always (much like a macbook) and only “woke” it when I was playing to avoid the super annoying noise upon boot….
I guess “be right back” would allow me to do the same? - would anyone disagree here?
I’m not sure that this is a software problem. I experienced this problem maybe 4 times over the years. When it happend it was persistent but I was always able to “fix“ it with a gentle clap to the QC. The last time I opened the QC (I am a Electrical engineer 
) and replugged the ribbon cables. since then it never happend again.
I’ve also noticed in the past that this behavior occurred when using an expression pedal.
I
This sounds interesting.
As my QC has (since its last SW update) not behaved in the described fashion again, I´m quite happy with it at the moment - still out of curiosity, where exactly would you “clap” the device if it was to behave like this asgain in the future?
I grabedv it by the foot switches lifted the front maybe 5cm and then stomped it gently on the floor. ( Case)
When performing this was annoying and the stomping helped without reboot. Therefore I assumed that maybe contacts are the problem.
Br
I also assumed it had something to do with higher air temperature. Also a sign for a bad contact.