Reverb in the loop issue

Im curious if anyone might have any thoughts on why my spaceman orion analog reverb pedal isnt working well in the loop of my butterslax?

When turned on, it makes a huge/very loud thumping sound. Once on, its very noisy (hissy) and the reverb cant really even be heard much.

it works fine in the loop my my marshall 2555x, and they both have a low level post eq loops, right?

the reverb is being powered by a pp2+.

Thanks!

Well because there is no return level and the amp has lots of gain in the return stage, you hear any noise or hiss a pedal has.

thanks dave!

what about the near heart attack inducing thump when turning on the pedal?