[Looking Good in Red]

So, lately my car has been running pretty good up until this morning.
On my way to a friends house, it started to sputter, almost like a misfire, however it didn't pull any codes. It isn't a bad sputter, just every once in a while. It only does it from about 2000 - 4000 rpms, not in idle or anything.
While I was waiting for her to come out of her house, I was just idling in the parking lot and I heard about 5 knocks coming from the gas tank/exhaust area. It literally sounded like someone knocking on it. I was wondering if the fuel pump would be a likely candidate, or could it just be bad gas or something?
Also, and I don't think this is it, but I have changed the plugs and wires recently, but I didn't get to change one plug yet... just haven't had time. I think this is the original plug and if so, it has 140k miles on it.
One more thing is that I recently had to replace an ignition coil because of a misfire, but that pulled a code, so I don't think that is my problem.
Any help would be apreciated.