Noise on channels 1 and 3. Replaced V1 and V3, no change.

[audiomason]

Problem:
Noise (like white noise or static hiss) on channels 1 AND 3.
Happens with or without guitar plugged in, FX loop in or out, reverb off.

Troubleshooting attempts:
Replaced V1 and V3 with new Mesa 12AX7, no change.
Checked all other tubes by tapping with a pencil, nothing unusual.

Channel 2 is crystal clear.

It seems like this issue should be related to V1 or V3, but apparently it's deeper than that. I'm going to call Mesa customer service on Monday, and will report what they say.

 

[sevycat]

Check the Phase inverter. It has a global effect.

 

[audiomason]

Didn't check the phase inverter because channel 2 is clean. I might give that a shot though just to be thorough.