Dear Tom and Ray:

I finally figured out what the sound is in my garage. Something on my 2009 Toyota Corolla is running when the car is turned off! I have heard it at various times of the day and night, and also when the car has been parked for hours. There is a noise coming from the driver's-side rear -- behind the tire. It sounds like a fan.

It runs for four to five minutes at a time, then shuts off. I called Toyota; they have no idea what it is and want me to bring it in. After taking it several times, I really don't want to give up the use of my car AGAIN. And it might not turn on until everyone has gone home for the night. Have any ideas?

P.S. The car runs fine.

-- Elaina

TOM: Well, first we have to chide you for hanging around your car hours after you've shut it off, Elaina. What are you, some kind of Corolla stalker?

RAY: It's probably the evaporative emissions system pump, Elaina.

TOM: Before we were concerned about pollution and smog and asthma and not being able to breathe and all that, all gas caps had pinholes in them.

RAY: That allowed air to enter the tank as the gasoline was drawn out. Otherwise, the gas tank would crumple in on itself, like a baggie that you sucked the air out of. But, of course, the hole in the gas cap not only let air in, it also let gasoline vapors out, and that created ... well, Los Angeles.

TOM: So, an evaporative emissions recycling system is now used on every car. It allows air to get into the tank but stops gasoline vapors from escaping. Instead it stores the vapors in a charcoal canister, and then purges them and sends them to the engine to be combusted when the car is started again.

RAY: What you're hearing is the evaporative emissions pump pressurizing the system. It does that automatically to check the system for leaks. If it discovers a leak, it'll eventually turn on your Check Engine light.

TOM: I'm guessing you have a sticky valve or some sort of small leak in the system. It should be covered under your emissions warranty.

RAY: So you can go back to your dealership and point them in the direction of the evaporative emissions pump, and ask them to check it out.

TOM: Or, alternatively, stop loitering in your garage, leave the car alone and don't worry about it until the Check Engine light comes on. Good luck, Elaina.