I have a 2003 4.0 FX4 4X4 Manual Tranny.
Ok I see there are alot of engine noise threads and I looked through several and dont see a description of mine..
Mine is comeing from somewhere in the front of the engine.. It sounds like (the best I can describe) safety pins in a jar shaking it..
Now it happens when I start it up and rev it.. it also happens when driving..
at first I thought it would be the idler pully or the tensioner pully.. I replaced those.. . then I thought it could be the alternator pully.. I replaced the alternator..
I just bought this truck, so i also changed the oil, changed the spark plugs, changed the tranny fluid and transfer case fluid.. The only thing left to change is both differential fluids..
It almost sounds like detonation, but the plugs looked ok when I changed them.. and so after my fluid and spark plug change i went out and beat the hell out of it.. i rode it to 6K rpm in first and second several times... It didnt blow up, but I also dont hear it when reving that high..
I can hear it inside the cabin when driving normally.. under 3K rpm..
I have read about the timing chain tensioners going bad.. but I also know you have to pull the engine to change to one in the back.... Can you just change the one in the front? i dont hear the noise in the back..
Here is a video: This video is the engine running with the belt off....