I've done a search on the oil can popping noise and all I get it is that it most likely the muffler. I took my 03 fx4 expy to the dealer to get the TSB done to fix my front 4 wheel drive clunking and howling noise which took me a year to get the wonderful dealer to fix it after I researched and found the TSB that fixes it and also told them about the popping noise. Those great knowledable service guys again said I'm nuts and they do not hear anything just what they told me about my 4x4 cluniking noise and I should try prozac and maybe I would not hear it anymore. Well, I'm eating prozac right now but you know the DAMN popping noise is still there. When I first started hearing the noise is was only after I stoped, turned it off and got out. POP, WTF? Then I started hearing it 10 min after I turned it off and was in the garage. POP, WTH? Now I hear it popping while driving. POP WTH? My point is, it is getting worse and someone here has to have a clue to WTH it is. It is starting to tick me off, 40k and a popping car. Do you think FORD dealers or service poeple surf this sight? If they do here is a message for you. YOU ALL SUCK AND CAUSE MUCH FRUSTRATION. I can't believe I pay you and still have to do your job for you guys!!!! I do still LOVE My FX4 EXPY though...