Have a howling noise on my 96 F150.
Starts after the truck has warmed up. Goes away when accelerating, and comes back on deceleration or coasting. Does not happen all of the time but is getting more frequent. I went under the hood to track the source.
Seems like it is coming from a part on the firewall nest to heater hose connections an AC. Dont' know what it is. Looks like fuel lines attached and hose going to engine manifold. Has black cap.
I never had an F150 before and am completely confused as to what this unit is. A friend said it was a sending unit, but for WHAT???

 

Check for vacuum leaks, and check your air tubes for emissions.

 

Check your pcv valve I've seen them make some weird noises. Not sure about the part possibly a Purge Solenoid Valve. A picture would help if possible.

 

It sounds like you are describing a vacuum log. It may be cracked or 1 of the caps may be bad. Check the vacuum lines also.

You could also be describing the MAP sensor

 

Don't know what it does but it line going into canister next to radiator.
Fuel line also attached to this canister . Vacuum line from part to intake manifold. Also, don't know what the purpose of can ister is. Looks some some kind of filter. If you are experienced with this 1996 Ford setup, Please help.

 

My 96 F150 has begun making a similar sound, so I will be interested to know what ends up being the cause.

 

Come on all you FORD mechanics. Somebody must know what that part is and what it does. Also, why is it making that noise

 

If it runs to the canister it's the canister purge solenoid.

 

Thanks to Just Call Me Sean
You identified the part perfectly. Canister vent solonoid.
Now, what the heck does it do and how do I stop the howling noise?
Does the canister need to be cleaned or replaced or the solonoid?
Kind of an expensive part.

 

It is howling because it is leaking. You will need to replace it.