When my car is idling I here what sounds like a misfire but it's very faint you can hear the normal exhaust note and then what sounds like a deep 'poom, poom' kind of sound, it's random and not very loud but it's definitely there. I don't throw any codes, and got new plugs and fuel filter, it it just me over listening? When you here the sound you can feel it to if you are sitting int he car, like I said its not loud and it's from the front of the car the engine seems to idle fine and can't hear any misses? Any ideas?