Humming E350

[F1bNorm]

And not a good hum!
The interior cab heater/AC fan is making a constant humming sound that varies with the speed setting. I don't think it's something rubbing against the squirrel cage blades. Does the problem sound familiar? Hoping for a quick fix! If not, It looks like the fan assembly comes out on the engine compartment side, correct? This is an 05/06 E350 cab.

Thanks for looking!

Norm

[Harvey51]

Leaves in the fan or even in the ducts could cause that.

[Andy1]

They hum when they don't know the words.