When I'm stopped at a stoplight my pickup makes a very low humming noise. I'm not sure how to describe it but it's a very lone tone, almost like a really low bass sound from a giant subwoofer. It only does this when in drive with the brake applied. If it's in neutral or when I start moving again press the gas it stops. I have no clue as to what it is. It also kinda makes this sound as I'm slowing down. The tach kinda goes up and down as I slow down and it starts making this noise in a pulsating manner. It's almost like something is not quite engaging/disengaging.

I don't know much about transmissions, but I'm pretty sure it's coming from there. Any explanation would be appreciated. It's a 99 5.4 with the 4R70W.

 

OK today when I was driving around it didn't make the noise. Maybe it's a function of the air temperature?

 

Nobody wants to take a stab at what this might be?

 

I am having the exact same problem. Have you figured it out yet? I'm planning on going to the dealer next week.

 

I haven't figured it out. It seems to only do it on pretty hot days (100+ or so). It's kind of random.