Zero loss effects loop cross talk/bleed through in Sovtek

[conjurer_of_riffs]

Hello,
OK here is the story. I have a sovtek mig 100h, some time ago the drummer of the band I was in installed the zero loss effects loop. The loop works great. I use the loop to integrate my Digitech RP1000 using the 4 cable method. This way I could maintain the sovtek preamp and use the RP effects both before and after the amp. I noticed a low volume distorted signal bleeding through when I would tune. I thought it was the pedal, but I did another test. I plugged cable into the effects loop send and one in the return, while the effects loop is engaged I removed the cable from the send jack. The noise is still present. I took my amp to a professional and he told me that the loop was installed improperly. So he restored the amp back to original specs and then installed the loop proper. Well the signal bleed is still there. Is this normal for the loop or is the amp causing it or is the loop still not installed proper? I have a schematic of the amp and a bad pic of the loop that I can email. I don't know how attach items to this post. Does anyone know where I could start or what I can do? I plan on taking the amp to another service guy but would like to have some info to give him when I do. I love the loop and possibly could live with the bleed through if that is just the way it is, but would rather it be silent when I tune.

Thanks for any info.

[RACKSYSTEMS]

Bleed is most often in the circuit of the amp not in the loop itself. Could be anywhere.

[conjurer_of_riffs]

Thanks for the reply RACKSYSTEMS. How could I test this theory that it is the amp circuit? When I bypass the effects loop with the bypass switch there is no bleed through. Shouldn't removing the cable from the send jack do the same thing? I have also saw on another post that a tube is bleeding some of the signal to the loop. Is that possible? Would someone just use a specific tube to alleviate that?