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'02 Honda Civic SiR.

Recording of noise, revving while parked. You probably won't hear it without speakers or headphones. It's best heard from the inside the car, and clearly coming from the front-right. I can hear it from the pulley area with the hood open, but I don't have adequate recording equipment to capture the audio.

The pulses increase/decrease frequency proportional to revs, not road speed. Nothing else makes any difference to the frequency or volume of the noise: fan, A/C, engine hot or cold, at idle or driving, clutch in or out, in or out of gear. All accessory equipment is operating normally (A/C, alternator and water pump. P/S is electric on this car.)

I have already replaced the idler pulley, tensioner pulley and serpentine belt. The tensioner spring action was smooth and quiet when pulled back manually.

What else could it be?

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  • Any accessory that runs off the belt (anything the belt turns). Buy yourself an inexpensive mechanics stethoscope to track the sound down....harborfreight.com/mechanics-stethoscope-63691.html
    – Moab
    Commented Feb 4, 2019 at 17:55
  • If all else fails, following @Moab's line of thought, you can also use a long shanked screwdriver, placing the handle against the bone just behind your ear to provide the same effect as a mechanic's stethoscope. You just have to be careful not to have any hanging apparel on your body which could get caught up in the drive mechanism of the engine.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Feb 4, 2019 at 19:35
  • Thanks, I've actually done that on bolts that secure the idler and tensioner pulleys. It actually seems loudest on the tensioner pulley, but that was already replaced recently (??). None of the other pulleys (alternator, water pump, A/C, crank) are free-spinning, so I can't just put the stethoscope on those.
    – autobottodoggo
    Commented Feb 4, 2019 at 22:19

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it's hard to hear the noise from your video, but if it comes from a slipping belt, you probably won't be able to hear it distinctly with a stethoscope / screwdriver, in this kind of case it could be difficult to identify the source this way.

If I were you, I would try to identify the nature of the noise (more like a whining slipping rubber or a whisthling failing bearing... As you said pulsating rubbing sound, it could be the belt slipping, but you are the most likely to know as you can hear it directly). I would also try to identify the source by simply listening to the engine bay (in case the stethoscope / screwdriver diagnostic didn't succeed as you expected), if it was possible, it could be hard to know from where really loud noises come from.

If you suspect that your belt could be slipping, you could check around the belt driven components for rubber dust and particles as a belt slipping around a pulley generally wear really fast, in this case you should find rubber all around the faulty component (assuming your engine has already run for an extended period of time under these conditions and your belt has worn enough). If you own an infrared thermometer, you could also measure the tempature of pulleys as the rubbing will increase temperature quickly.

You could measure the tension between the positive and negative terminals of your battery with the engine shut off, and then running, generally, you will hear that your battery should be around 12.5V when it's fully charged, and then the tension is supposed to raise by between 0.5V and 2V with the engine running, a low value could indicate that the alternator is not charging correctly, for example in case the belt is slipping around its pulley.

If you still cannot troubleshoot your issue, you could eventually try to remove one of the belts assuming it DOES NOT drive essential components like water pump (make sure it only drives A/C for instance), it could show you from which belt the noise comes from, or at least reduce the list of potentially failing components.

In case the cause of the noise is the belt slipping around the alternator, it does not always indicate that the alternator is failing, it could also be another electrical component that is failing. Before changing it at least check the battery.

Hope it helps.

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