If we're talking about a fat gain rebound? I'd say that does not exist. I think ppl just end there diets and stop stims and then eat like a jackass and make up something like clean rebound or whatever to be a excuse.
Again I'm not sure if this is what your talking about, but Ive never seen it. As far as I know, clen has no effects on hormones like insulin, gh, thyroid or cortisol. It dosent effect testosterone or estrogen, nothing I can see causing some kind of rebound