Loud buzz or vibration (1 Viewer)

[TTownEP]

I just heard this morning, for the second time in about a month, a loud vibration noise that I would best describe as similar to one of those little oil-less pancake air compressors. A loud buzz if you will. I've only heard it while moving, but speed is not relevant, nor engine speed. The frequency does not change. It fades in (volume), plateaus for a few seconds (2-5) and then fades back down. I got probably 7-8 cycles this morning, while driving at 25-30mph in my neighborhood.

My initial thought was AHC, as it was the obvious pump or compressor that could make a noise like that, and it sounds like it could be down near the lines or the accumulator under the driver running board, behind me but in front of the rear axle. I have heard the AHC pump under normal conditions, obviously, and it doesn't sound like this. It's much higher in pitch normally.
AHC operation seems unaffected. I don't see any leaks, and I haven't had/done any work on any systems lately. I did flush and fill the AHC fluid at about 100k miles, about 48k ago.

Does anyone have any ideas what this might be?

Edit: 2011 LX570

 

[grinchy]

something in the amplifier cooling fans. The amplifier is under the US driver seat (left hand).
or maybe the seat cooler fan.

 

[El Skywalker]

I get a similar noise when my cooled seats are running.
Took awhile for me to figure out where the noise was coming from.

 

[TTownEP]

It's outside the cabin by my ear. Definitely louder than the cooled seat fans.

 

[CharlieS]

Maybe something to do with the braking system. Accumulator or something like that. I don't notice it on my '16, but it was pretty loud on my '13.

 

[bloc]

Is the exhaust rusty at all?

 

[TTownEP]

Is the exhaust rusty at all?

No, it was a Florida car, and now South Alabama.

 

[montegofd3s]

Where you braking or just moved your foot to the brake pedal? Maybe the ABS pump. I can hear mine pretty clearly, but I am use to it as the 100 series does the same thing.

 

[TTownEP]

Where you braking or just moved your foot to the brake pedal? Maybe the ABS pump. I can hear mine pretty clearly, but I am use to it as the 100 series does the same thing.

No, I would not associate it with braking. I did apply the brakes and the throttle while this was going on, but the sound was not affected. I was leaving my neighborhood, which is fairly hilly and curvy for this coastal area, so even with up and down and left and right turns, the noise was on its own schedule. Speed varied from 25-30mph.

It literally sounds just like this compressor, including the pitch and frequency, except that the volume ramps up from nothing to full volume over 2-3 seconds, holds at max for 4-5 seconds, and then ramps down again.

 

[TTownEP]

What about SAI? When it goes out, does that pump get pretty noisy?

 

[montegofd3s]

No, I would not associate it with braking. I did apply the brakes and the throttle while this was going on, but the sound was not affected. I was leaving my neighborhood, which is fairly hilly and curvy for this coastal area, so even with up and down and left and right turns, the noise was on its own schedule. Speed varied from 25-30mph.

It literally sounds just like this compressor, including the pitch and frequency, except that the volume ramps up from nothing to full volume over 2-3 seconds, holds at max for 4-5 seconds, and then ramps down again.

So something like this?

 

[CharlieS]

SAI fans sound like hoover vaccum cleaners when working correctly, but can make more noise as the (air pumps) fail. As I recall SAI only runs at startup. Could be wrong though.

 

[TTownEP]

So something like this?

Yeah, could be. It's hard to get a sense for the volume, but I'd bet what I'm hearing is much louder than that.

I'll have to jump out and check the next time I hear it. That's the best option I've heard though. I wonder if it throws any trouble codes before failure, or if my generic code reader would even find those codes?

Thanks for the theory, I will pursue it.

 

[montegofd3s]

Yeah, could be. It's hard to get a sense for the volume, but I'd bet what I'm hearing is much louder than that.

I'll have to jump out and check the next time I hear it. That's the best option I've heard though. I wonder if it throws any trouble codes before failure, or if my generic code reader would even find those codes?

Thanks for the theory, I will pursue it.

Failure in the 200s is rare, but much more common in the 100 series. You may just need a brake bleed. If you sit in your driveway and push on the brake pedal a few times you should be able to activate the accumulator pump. Maybe someone can do it while you listen? Generally it does not throw codes, but if it does fail it will set off a warning buzzer. If you pump the brakes like 30 times in a row or crack a back brake bleeder you will know its running and the buzzer will go off.