[junkgear]

It sounds like the level or gain coming into the 11R guitar input is hotter than what you would get from the guitar itself. You probably don't notice it on low gain amps since there is still some headroom, but on amps that already are boosting the gain a lot, the extra boost up front will cause noise.

Try picking a clean amp in the 11R and plugging your guitar directly into the guitar input. Play something and take note of the volume of the guitar. Now plug the ES-8 into the guitar input of the 11R and your guitar into the ES-8 and play the same thing. If it sounds louder, then you need to try and pull the level down on the output of the ES-8 that driving the guitar input of the 11R.