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Discussion Starter · #1 ·
My car has an intermittent electrical "whirring" sound that last for a few seconds and goes on and off while I'm driving. The sound comes from the front driver's side and seems to be related to the brakes... but happens whether I'm braking or not.
It will also sometimes happen shortly after I shut the car off too.

WTF is this? Anyone?
 

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Brake booster vacuum pump. I had an issue recently where mine would run constantly with the ignition on, no matter if the engine was on or off. If you hear it intermittently I would say that is normal. You should hear it when the pedal is depressed, but I suppose it could happen other times as well?
 

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Discussion Starter · #3 ·
Brake booster vacuum pump. I had an issue recently where mine would run constantly with the ignition on, no matter if the engine was on or off. If you hear it intermittently I would say that is normal. You should hear it when the pedal is depressed, but I suppose it could happen other times as well?
After looking it up in my Haynes manual, it seems that only the diesel model has a vacuum pump. Mine is a petrol gas model. The whirring sound happens more and more often now.
Any other suggestions?
 

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Are you sure? Brake Vacuum assist pump should be installed on all models. The vacuum assist pump is supposed to maintain brake circuit vacuum when the engine is off or when engine vacuum is low (i.e. Cold starts and on throttle). There is a vacuum switch up top located between the air box and the DS headlight that activates the pump when vacuum is low. If there is a leak it will run constantly, but if no leak is found then it maybe the switch.

Vacuum pump cycling is normal when pushing the brakes with the engine off, key in position II. There's an issues if the vacuum pump runs on and on.

http://www.volvoxc.com/0/resources/how-to/pdf/power-brake-booster-replacing.pdf
Checking the power brake booster
Depress the brake pedal several times until it feels stiff.
Hold the pedal down. Start the engine. The pedal should travel and feel softer.
Release the brake. switch off the engine. Wait 1 minute. Then depress the pedal. The pedal should still feel soft but should become stiffer when it is depressed several times.
There should be no leakage between the vacuum hose and the terminal at the power brake booster.
There should not be any leakage between the master cylinder and the power brake booster.
Check that the stop lamp functions.
If the stop lamp switch has been modified or changed after installation of the master cylinder and power brake booster it must be readjusted.
Similar test with the vacuum pump. Instead of starting the engine, you turn the key to position II.

Year?
Model?
Miles?
 

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There's definitely a pump in the petrol models. Mine has one, and my switch for it was acting glitchy recently remaining ON as long as the ignition was in the ON position no matter if the engine was running or not. You SHOULD hear the pump intermittently at random times, but not all of the time. There's a plug to the switch at the top of the engine right at the very front, with it disconnected you shouldn't hear the pump at all. I don't have a picture at hand unfortunately of which plug that is. But that's how you can test out of that's really what you're hearing.
 

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If it's an electric "whirring" sound, it could also be that stupid little fan behind the climate control. Mine is bad and is constantly going on and on as soon as the accumulator starts going. I don't know under what circumstance it would go on and off, but just something to keep in mind, and the other guys on here might definitely be correct about that vacuum pump. Try depressing your brakes a couple of times, listen to the center console to see if it's coming from there, test everything out.

Good luck!
 

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I know not long after getting my '04 S60 almost a year ago, I'd hear a faint running fan often after long drives, when I'd park. Turned out to be the ECM/TCM box fan that would run for a few minutes after turning off the car. Once I learned what it was, I think I began ignoring it, lol! Sometimes I think I'm hearing a small faint fan in the HVAC system, and no other fans (normal vent system fan, or engine related fans) are going. Weird...
 

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Discussion Starter · #9 ·
Ok so here's what's going on now.
Whenever I press the brake pedal, the whirring sound (like a cd ejecting, but REALLY loud) happens for about 5 seconds. EVERY damn time I touch the brake! WTF is this? The brake booster switch, the vacuum lines, or the pump itself?
I am ready to order parts but I'm not sure which of the parts is failing.
Thanks in advance for your help guys and girls!
 

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Before throwing money randomly at the problem, check for a vacuum leak. The auxiliary vacuum pump should only run when there is not enough vacuum in the braking system, such as when the car is first started, heavy brake use, etc. If it kicks on every time you touch the brakes, it seems like the engine can't supply enough vacuum, possibly due to a leak in the system. It could be as simple as a cracked or deteriorating vacuum line. If the pump runs and then shuts off after 5 seconds, it sounds like the pump itself and the low pressure switch are working. A lot of times when the switch fails, the pump will run continuously, causing it to overheat and fail, but this does not sound like it is the case here.
 

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Are your speakers off when this happens? If your speakers are on, it could be electrical noise getting into your sound system.
 
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