Just picked up this 2002 Liberty limited 3.7. I've replaced the muffler and tailpipe and donut gaskets. It still has an intermittent loud rumble when I push on the accelerator. I'm having trouble figuring out where it's coming from because it's intermittent. I'm not sure if it's a manifold gasket or maybe the v-clamp above the cat? Doesn't run rough or stall and no codes. Almost sounds like a pressure build up or something, it's kind of hard to explain. Anyone had anything similar? Any tips for helping me pinpoint it?