Humming noise coming from car

Hello, I recently hit a pothole and damaged one of my custom wheels to the point it was dangerous to drive on, I could not find a matching wheel for the car (2007 Chevy HHR) and had to drive on the donut spare for about three days, I put the spare on the rear passenger side, So for about three days I was driving with an 18" rim on one side and a donut spare on the other. I noticed a humming sound when I get to 40 mph. I thought it was just the sound of the tread on the spare, But I have since bought new rims and tires and the humming sound is still there. Again, I only hear it when I get to about 40 MPH, below that, no sound at all. The car seems to shift smoothly. Could driving on two different tires on the rear end have screwed up my differential? Thanks and I know driving on a spare for that long is not optimal, but time and money and lack of being able to find a new rim on such short notice was a factor. Thanks again.

Isn’t the HHR a FWD vehicle?
If that is indeed the case, then the absence of a rear differential allows you to rule out differential damage. Unequal size tires/wheels on the rear would have no effect on the differential of a FWD vehicle.

As to what the source of the noise might be, all that I can come up with as a possibility is a damaged wheel bearing. If the pothole hit was hard enough to ruin a wheel, it is very possible that it caused damage to the wheel bearing as well.

Agreed. Humming or growling is a sign of a worn or damaged wheel bearing. Also, did you get an alignment done? A pot hole strike bad enough to damage a rim probably tweaked other suspension parts and threw the alignment out of whack.

HHR’s are front wheel drive and I believe you damaged a wheel bearing. Better get that checked out.

I agree with the comments above that you want to have the suspension checked for damage and have an alignment done. You definitely don’t want something to fail at highway speeds and you don’t want to wear out any tires prematurely.