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2007 Dodge grand caravan possible misfire when rains

I have a 2007 Dodge Grand Caravan with the 3.8 v6 with 93,000 miles on it. It runs quite well, other than I have noticed that when it rains I can hear what sounds like poping or possible rattling coming from rear of the van, I am assuming this is coming out of the exhaust, but only when kind of cruising along with motor under light /no load just keeping speed on flat road. If under load or coasting sound instantly disappears, and sound is intermittent, only once in a while, and only when it rains outside, if dry never happens,

I replaced spark plugs and wires, tried to replace coil pack, but new coil pack was bad from the start as with new coil pack it ran like it was missing a few cylinders, assuming one of the 3 coils was bad, put old coil pack back on and then runs smooth as a kitten.

With new plugs and wires the odd sound is not as often but have heard it once during last rain storm.

Just wanted to get opinion from all the great folks here on where to go next, I am thinking next try another new coil pack. any other ideas?

also just had a recent oil change along with air filter change. (change air filter every other oil change)

Thanks in advance,