Squealing? Sounds like it's harshly compressing your signal. The pedal it self may be the issue. If you're running an OD pedal into clean and it's squealing i would imagine the tone can't be that great. You may want to try to use your high gain channel on the messa and then adding the pedal you are using but turn the gain down on the pedal. Just to give your high gain channel a little boost.
I am using the high gain channel, I tried turning down the level on the pedal but it’s not giving me enough gain. I was thinking of getting a Maxon OD808X any experience with the pedal?