rhythmic hum from engine at highway speed

[rtom]

Does anybody else hear this?

My manual transmission 3-door LB with about 11000 miles on it is making a humming sound that modulates with a cycle time of 3-5 seconds. I don't know the right musical terms, but here's an approximation:

HUMMMMMMmmmmmm HUMMMMMMmmmmmm HUMMMMMmmmmm

where the all-caps means louder and small-caps means less loud. It's a vibration of some kind that is coming from the front of the car, probably the engine or transmission, and it only occurs under load and at 55+ mph. If I push in the clutch, it stops.

I know funny little noises can be very hard to diagnose, but thought I would ask. I don't think I heard this when it was new.

Also, after the second oil change it is less loud.

[R2D2]

Mine has done that since the day I took delivery. Just as you say it only occurs at 55 plus. I have an auto which I suspected had something to do with it, but apparently not. Not a big problem for me but I too found it interesting.

[craigq]

My automatic sedan also has the 'highway hum'. I can't recall if it has it with the winter tires on or not. Still using the OEM Potenzas for the spring/summer/fall...

[Astroman]

What tires do you have? Mine did that at first with the 15" goodyears, stopped when they wore down a bit and now I only use the stockers in the winter.

[Yaris Hilton]

Most likely hum from two tires that are of slightly different diameters, or rotating at slightly different speeds from a slight curve of the road, so the hum is slightly out of synchronization, alternately reinforcing and cancelling.

[brg88tx]

my auto sedan does this too. imo it's not from the tires. i think it's from the engine or transmission.

[Yaribusa]

I have about 500 miles on the new Yaris, and I noticed this last night. Mine is a 2010 3dr Manual and I noticed it at about 55 MPH. The noise did go away when I engaged the clutch. It kind of reminded me of a small airplane, but it was not loud enough to be an issue at all.

[ajae]

I have the same hum on mine as well. I don't always notice it, so I wonder if it's some kind of resonance being set up somehow in the engine/tranny/torque combination. 75,000 miles on my '07 Yars.