Strange humming sound

[Welder Dave]

I have 94 Ford L9000 with a Cummins M11. It's common to here slight air leaks when you shut it off but today it made a weird humming sound but not every time. I'm guessing it could be something air related as well but maybe something electronic? It doesn't seem to affect anything just curious what it could be?

 

[Ronsii]

The humming sounds I usually hear related to air brake systems are generally the regulator to the accessory tank when the tanks are about equalizing from the main.

 

[grandpa]

Sometimes when your park valve gets tired it will act like that. Try resetting the valve and see it the sound changes or goes away.

 

[funwithfuel]

It might be electric vacuum pump for hvac controls. Not sure when they transitioned to stepper motors.

 

[funwithfuel]

The humming sounds I usually hear related to air brake systems are generally the regulator to the accessory tank when the tanks are about equalizing from the main.

I've experienced this, but for my experience it was like a shuttle shifting open and closed and the sound corresponding to the valve. Like wah wah wah

 

[Ronsii]

I've experienced this, but for my experience it was like a shuttle shifting open and closed and the sound corresponding to the valve. Like wah wah wah

Yeah, we got a pup trailer that'll sound the wah wah for a few minutes when it get real close to equalizing tanks.

 

[thepumpguysc]

U guys ever see that Howie Mandel skit/joke about going to the Dr. about a strange humming sound??
See if u can find a ut video of it.. You'll LYAO & NEVER forget it..

 

[Truck Shop]

A 3030 parking brake air chamber leaking back from emergency side to service side putting air in reverse against R12 relay valve can cause a hum at exhaust port.

 

[funwithfuel]

A 3030 parking brake air chamber leaking back from emergency side to service side putting air in reverse against R12 relay valve can cause a hum at exhaust port.

He said its when he shuts it down, certainly hope the brakes are set before he walks away from it.

 

[Welder Dave]

It seems like it's coming from under the hood or the dash area and the parking brakes weren't on when I heard it. I was parked in a level area that was a little soft so it wouldn't have rolled anywhere.

 

[funwithfuel]

So your brakes were released?

 

[Welder Dave]

I shut the truck off while I loaded it and didn't put the brake on because I was in soft sandy material where the truck wouldn't move anyway.

 

[Ronsii]

That is known as 'sand chocking' might be MSHA approved for use in Canada

 

[Truck Shop]

It will still feed back to dash valve, And some people pull the red valve for parking folks.

 

[jSCULLy]

isn't it because of the break stuffs?