Hey scotty, at Idle my car's exhaust sounds really weird (like a rumbling noise as its going to die out)but when driving it sounds as it does before. I can't figure out what is going on.

well, if engine runs bad at low speeds, exhaust will sound weird and engine will idle incorrecty. Start with this cleaning video, pray it's such an easy fix https://www.youtube.com/watch?v=NWCKvU2FmDc