None of the similar threads were conclusive for me, and I have a concern so here's my (hopefully) very descriptive explanation of a sound that started today. Car's a 2005 Prius, 92K miles (and our dream car! No problems so far!). Today, while driving, I begin to hear a sound from the engine compartment with which I am not familiar. Every five seconds, there is a quiet whirring that lasts about 3 seconds or so. It sounded vaguely like the sound you might hear when you are on the phone calling someone else and you hear the "phone ringing" effect. Had cruise control on. Turned it off. Had the heat on and rear defroster. Turned them off. The sound continued. Every five seconds. There was no noticeable effect to the vehicle. She kept driving just fine. When I got home and turned the car off, I heard the car do the usual sort of powering down thing it does. Then I waited. And sure enough, for a little while... every five seconds, this little whirring sound and a click. I listened to it do this for three or four times, then I took my bags inside, came back out, and it had stopped. Any clue what this sound is? Should I drive to the dealership right now?
Sounds like the brake accumulator pump. If it's running that often, and you've not been using the friction brakes, I suspect something's wrong. Check the level in the brake fluid reservoir to see if there's a leak. The car should log a diagnostic troubleshooting code - DTC - but it's possible the brake accumulator pump on-time isn't quite long enough to trigger the code. One of the brake DTCs suggests that it can also occur if a brake is dragging.
Does the whirring sound come from down around the driver's foot well? Is it sort of a ratcheting sound? If so, I also suggest that it is the brake accumulator pump. This pump normally runs every third time or so when you press on the brakes. If it is running cyclically, it suggests a pressure leak. Tom
It was coming from near the top of the engine compartment. It has stopped making that noise. Still no change in the way the vehicle behaves.
sounds like brake accumulator pump... i've had that sound for a long time.. i'm now getting codes and warning lights with codes saying the accumulator isn't getting enough voltage... a good sign for me to just replace it before it does completely fail...
