Yellow box MXR chorus, right? As I recall, from 35 years ago, both the chorus & analog delay were hiss monsters. Sorry I don't have a suggestion. Back then I had a customer who had both, of course didn't like the noise, he just shelved the effects and moved on to other gear. Unless you can come up with a cookbook fix for the chorus, I'd pass it by. I don't remember the MXR was any great shakes, and most people were picking up the Boss CE2 chorus just about then, and the CE3 just after that.