I have a 2009 Toyota Yaris with 35,000 miles, and fully up-to-date with all the 5,000-mile usual maintenance checks [no prior problems]. Driving on a hot day from San Francisco to Los Angeles, I hit Bakersfield and the car started to make a high-pitched whining noise, which got louder with the accelerator and softer when I took my foot off the gas. I thought perhaps the car was overheating and let it rest for a while, and checked the coolant [which was at a normal level]. I finished the drive to LA and stopped by the Toyota dealer who said it must have just been the fan given the hot weather. The noise went away overnight, but the next day I was driving around town when it was overcast and cool, and even driving locally, the car made the whining noise intermittently, especially loud at low speeds like coasting in a parking lot, and the noise has been getting louder and sounding more pathological–not like a normal engine or fan noise, but like a truly problematic high-pitched straining sound. Sometimes it comes on when I start the car, sometimes restarting the car makes the noise go away for an hour or two. It sounds almost like an electric razor being whipped around like a numchuck - a hitch pitched whine that is rotating in the engine and speeds up with the accelerator and calms down but doesn’t go away at a stoplight. Perhaps I finally ran over my neighbor’s annoying kitty. But today’s latest Toyota mechanic also couldn’t figure it out because the noise didn’t start when he turned on the car and didn’t restart on his test drive, but only a few hours later after I’d driven the car around town. Any ideas?
See if your mechanic would be willing to take a look while it is happening, so when it starts, stop on by the shop. It will probably get worse, but it would be better to find the source of the problem than waiting till it breaks and risk being stranded.
Does Any Vibration Accompany The Noise ?
I see, according to Toyota, that some 2007 - 2009 Yaris vehicles make an “abnormal noise and vibration,” have had separation of the rubber insulator in the left engine mount. The fix is to replace the left mounting insulator.
Anyhow, inspect or have the mount (It bolts to the top of transmission case.) inspected for separation. Toyota issued a bulletin to their technicians, covering this matter.
Deterioration of that rubber would allow normal engine/transmission vibration (and noise from metal-to-metal contact) to be telegraphed directly to the car’s body.
CSA
It could be something as cheap as a glazed serpentine belt. since it changes with engine speed. Pour a little water on the belt and rev the engine and see if the noise is gone. Replace the belt. Don’t use belt dressing. It attracts dirt and causes the belt to wear even more.
I suppose that it is possible that a diode is going out in the alternator, although usually the noise is constant. However, it is possible that as the alternator warms up, the temperature of the diode increases and causes the whine.