Whirring noise from under the car after it warms up

DUNBAO

MEMBER
2007 LEXUS RX 350
3.5L
V6
4WD
AUTOMATIC
186,000 MILES

I can hear some whirring noise coming from under the car after driving it for a while. I put the transmission into parking and turned off A/C and I could still hear the noise, sitting inside the cabin or standing outside. The only thing I'm kind of certain is that sound is not coming from the engine compartment. What parts of my car do I need to further investigate?

Tuesday, December 10th, 2019 AT 11:07 AM

4 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

Is there anything that changes the sound? For example, if you rev the engine? Really, there isn't much under the vehicle that can cause that kind of a noise. However, if you have a catalytic converter starting to come loose internally or partially plugged, it could make a forced air kind of noise. Also, a fuel pump issue can create a strange noise.

Let me know. Also, let me know if there are any driveability issues when this happens. One last thing, can you tell if the noise seems to come from the rear or front underside and is it possible for you to record the noise and upload it for me to hear?

Let me know.

Take care,
Joe

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Tuesday, December 10th, 2019 AT 7:34 PM

DUNBAO

MEMBER
2 POSTS

Hi Joe,
Thank you for the advice! The noise doesn't seem to change in volume and pitch as I revv up the engine. Actually the sound is kind of weak sometimes I can barely hear it. So if you revv up the engine it'll get coverred up by the backgroud engine noise. The sound has an on and off pattern that usually lasts 2 to 3 seconds with a 3 to 5 seconds pause in between. It seems to be most noticeable when I stand by the rear wheel on the driver side. So I suspect it could be a worn out fuel pump. Power steering also could be the problem because it's been over 5 years since the fluid was changed. PSF flush is easy. So I'm going to try that first. If the noise persists after that I'll further my investigation on the fuel pump and catalytic converter as you pointed out. I guess I'll need to get a stethoscope and lift the car onto jack stands in order to do that.

The sound is not accompanied with any drivability issues. Actually I can't even hear it at normal driving speed because of the road noise. I tried to record a video today. But it didnt work out. As I mentioned earlier the sound is weak and my phone's mic is not as sensitive as my own ears so I end up getting just the engine idling noise. Another thing is today's temperature is high and the sound seems to be even less audible in warm days. If temperature drops in the next couple of days I may be able to get a clear recording of the sound.

Thanks again for the follow-up! And I'll keep you posted with my findings.

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Friday, December 13th, 2019 AT 12:49 AM

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Let me know what you find. Since you hear it closer to the right rear wheel, there really isn't a lot there. As you already mentioned, the fuel pump can be heard back there. If you have an air ride suspension, there could be a leak. I'm trying to think of other things back there that could cause what you described. There really isn't that much.

As far as a the PSF, I would tend to think it would be more toward the front of the vehicle. Regardless, let me know what you find. I'll keep my eyes open for your reply.

Take care and have a good weekend.

Joe

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Friday, December 13th, 2019 AT 6:42 PM

JIS001

MECHANIC
3,412 POSTS

There really isn't anything on the driver side but the transmission. I would suspect 2 things. Either a bad alternator or water pump. If you open the hood up can you still hear the sound? If you do can you record near the alternator on the passenger side. While the sound present unplug the electrical connector at the alternator. If it goes away then the clutch in the pulley is bad. Very common problem.

If okay then check the water pump pulley for play. Use a pry bar and gently put pressure from behind to push outward. If the pulley moves then the water pump bearings are going bad and will also cause that whirling sound. Let us know on those 2 tests.

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