F-30 loud white noise/static while using effect loop

[scout_genesis]

I just configured my pedal board so the mod pedals (delay, chorus, volume pedal) run in the effect loop of my F-30 (4 cable method). After hooking it up for the first time, I'm getting a unacceptable amount of white noise from the amp, that sounds like FM radio static. When I bypass (unplug) the loop, the noise goes away. When I ran the same pedals in front of the amp input it was relatively quiet. I'm using the same settings on the amp as before. I also ran the same pedal configuration in my Mesa TA-30 and I don't get the noise. Any idea what's going on or how to fix this?

 

[scout_genesis]

Here’s some further info on my tests. Swapping out each of the preamp tubes with another tube didn’t solve the problem. The noise is there when I run a single cable in the loop with no pedals, so it’s amp-related and not a result of the pedals that I was using. As soon as I break the circuit in the effect loop the noise stops. Also, when on the clean channel the amount of noise decreases slightly when I turn the volume all the way up on the other channel.

 

[scout_genesis]

I tried a few different things last night and the problem was intermittent. I swapped out all the tubes and the noise issue is remedied so far. If it's not tube related I'll address the issue with a technician