Mysterious hissing & humming

I have a 2009 Corolla XLE with VSC with 1500 miles on it. One day I heard a humming sound and found it to be coming from behind the rear left tire, along with a hissing sound. It was not the tire losing air. When I turned the key to the On position, the sounds went away and I have not noticed them again. Any ideas?

Possibly something to do with the evaporative emissions system? If it happens again ask your Toyota dealer about it.

Time to read the Owner’s Manual!

Recently, I read the manual for my friend’s new RAV-4, and I found some interesting information that might be related to your situation. In the RAV manual, it stated that, after the car has been sitting for more than…4 (?) hours, the vehicle’s evaporative emissions system goes into a self-check mode to test for leaks. On the RAV, the manual states that a loud humming noise will be heard underneath the car, in the vicinity of the driver’s seat when this self-test is running. And, if the engine is started, the self-test will abort.

I suggest that you check for similar info in your manual as it could be a similar function, albeit with the noise emanating from a different area. Whenever an issue arises with a car–especially a new one with which one is not yet familiar, checking the manual for relevant information should be the first step.