I think I notice that this happens usually after I drive it through the rain. I don't slow down while driving during the rain, I still drive normally as I would when dry, thank you Michelin PS2's, I will still drive in manual and open her up here and there.

So after its rained, and I drive during a normal sunny day, I can hear an odd purring or type of burble which sounds like it is coming from the engine and heard through the dash. You pretty much cannot hear it standing outside though. It doesn't even coincide with the a/c because it will make the same noise with it on or off. Notably, I can tap the gas pedal and the revs will rise, along with the engine spin, along with the exhaust sound, and ALONG with that deep purr or burble. This sound is present even when the car is idle. It will purr in accordance with the engine rev.

It would almost seem as if there is something loose in the intake plenum. BTW, I have the Ztube and Motordyne plenum. Other than this odd sound that seems to come from driving through the rain, the car sounds absolutely normal on regular days.

I had wondered if the plenums plastic bolt spacers could somehow break and rattle, I have a "1st" gen plenum...and I asked Tony at MotordyneEng, and he said that is unlikely. I will have to agree with him b/c like I said, the normal days I do not get this sound at all.

Do you think that the intake ingests some water? Does an engine make a sound like this? The car still feels normal/powerful whether dry or wet.

So essentially, this sound really worries me. I feel as if soemthing is wrong. I really don't even know if I can record this sound correctly to show you guys.