Gotadoras pounding

Hello friends:
I consult you I have a megane K4M engine, I never pay attention to it but now listening to it with more attention this very dulling as if they hit drippers, when I do it and let it loose manually of the butterfly, the pounding is spilled, a few months ago I sent it to change the belt. My question is that when they changed the belt if they left me a little away, this can be hiding the noise or not. I hope you can help me.