hooohhh gosh!!! happened to me too!!!
Just switched on my new HD500x (2 months old, fw 2.62, NO new expansion pack), connect my Strato with EMG pickup, select <DG SOS> patch (from CustomTone) and start some practice...... after 5 minutes of test...... THE NOISE... at very high volume...... I can't explain if it was like larsen or like white noise..... !!! something similar when you touch the tip of the guitar jack but at very high volume and tone
I was just playing my guitar and moving the pedal (for SOS effect)...... The strange thing is that I was practicing yesterday for two hours in the same condition without problem... and also.... I have switched the 500x off and on again and play without problem!! strange....
well.. the setup:
-Strato in the guitar in
-Balanced out connected to the mixer, input fader on the mixer at 5 (0db), MAIN output fader OFF
-Un-balanced out L (Mono) connected to my little Fender Amp, Amp switched OFF
-Using headphone as monitor connected to the mixer
I'm sure that the noise come off from the 500x because before to switch it off I've disconnected the headphone from the mixer and connected to the 500x, disconnected the guitar and all the cable... but.....same noise
I'll test the exact same condition in the next day... to see if it happen again (and for practing!!)
NOTE: before you ask..... I've installed new FW(s) with the option to delete all patches and after the installation I've done a global setting reset and pedal calibration, than download my previously saved setlist.... It's the first time in two months of life of my 500x...... hope it'll never happen!!!!
Rino
EDIT... forget to say ... Global EQ was/is OFF