rain and tapping noise.

Hi,

Well I bought my jeep a little while ago. Fixed the entire exhaust system (headers too) because it had some nasty leaks. Now, the motor always had a little bit of tapping. It would be quiet for about 20 seconds on start up, then it would do start its faint tapping. Does it at idle, however it goes away after about 1500 rpms. I have read that it could be a stuck lifter or piston slap. But here is the twist, last night it rained hard. I have hood vents in my hood. So i came out this morning to start it, and the tapping noise was instantaneous there on start up. louder this time. I was like wtf. I turned it off. started it again, the noise was gone, but slowly came back after about 20 seconds or so (quietly) just as normal. Now what would rain water do to cause that? or is the rain not even related. I checked my oil level, to see if by chance water came in, level was fine. By the way, my vents sit right over my diz and tps, and cps sensors/plugs. It is just weird, that it does it all of a sudden after a hard rain. I turn it off, start it again, and its normal.

Any input?

thanks

Probably leaking plug wires or dist cap, most likey on the loom or where plug wires come close to each other or any metal part. You can usually spot it in the shade or dark. Try misting the cap & wires with water and see if you can make it happen again. This would sound like tapping and would be in addition to any valvetrain or piston noise. Just means you need new plug wires and or dist cap. While you are there replace the rotor too.