i have a 96 explorer with 4.0 L. i have a k&n complete intake system.when truck idles for long time i get a humming sound from the intake. goes away when engine is revved. notice it more on hotter days. what could it be?

replace your idle air control assembly. the noise is caused by air flowing through the IAC, replacment is the only remedy, many fords have thise problem.

I had a '97 Explorer with the 4.0 V-6... it did the same exact thing on hot days and I have heard it from other Explorers sitting in traffic... it has nothing to do with the non- factory cold air intake kit you have.... it's just something that happens on these models... it drove me buggy... but Ford never could solve it and it never was harmful... so just live with it I guess !!! I always assumed it had to do with the shape of the intake manifold !!!