ill try and break it down as best as i can, i have a 88 trans am gta auto 305 for the past 2 years my car has been making a very annoy "humming" sound, sounds like it is coming from the front passenger side area,
when it happens: when im driving any speed 5mph or higher without gas, when i give it any touch on the pedal it goes away, ive put the care in neutral and just coast it stilll "hums" if the car is just idleing there is no "humming" sound.

what could this be i have taken it to people and they cant seem to find the source, please help

 

It wants to sing along but it doesn't know the words.

Bad tire, bent wheel, worn bearings, etc.

Does the sound change when you turn left/right?

Sometimes sound transmits itself in strange ways throughout a chassis/unibody.

I had an old '62 Catalina that had a nasty rattle. To the driver, it sounded like it was coming from the right rear. To the passenger it sounded like it was coming from the left rear. The passengers in the back seat said it sounded like it was coming from the front corners. Hmmmm.....Found out the dome light mounted in the middle of the roof was loose.

 

No makes no difference in steering left or right, only happens when my foot is off the gas, second I give it alittle gas the sound goes away, dosnt matter if I get it just an extra .1 rpm the sound goes away

 

so i think i found the issue, looks like where this nut connects to the headers has rusted and is leaking air out, i blew smoke into a hose and it comes out there i dont think its suppose to do that, plz look at pic