So after I shut off the ignition and sit in the car for a bit I hear this humming coming from what seems like behind the main console, lasts 2-3 seconds. Got used to it in my 98 and picked up a 97 and does the same thing. Unique to the LS I am assuming. What is this?

 

I've noticed it too. Pretty sure it's the A/C vents, possibly a calibration procedure. On another note my infiniti does a throttle body calibration when you shut the engine off and makes some funny noises from the engine bay as the throttle plate opens all the way then closes.

 

Same thing here.

 

From another thread/forum:
"That the noise from the evaporative system purging and stabilize the vapor from the fuel system. You will hear the same noise after the car sit for over a few hours or over night also"
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I think I may have heard this sound a couple of times also. And it's different than when the gas vapor purge pump is running. That usually happens right when I turn the car off, and then I notice when my headlights turn off after a few seconds, that sound goes away.

But the other day, my RX had been parked in the garage for several hours and I was going to close the garage door before retiring to bed, and I heard this noise that I couldn't tell what the heck it was.

I thought maybe something that was stored in the garage had been turned on or something and I walked around the car trying to locate the source. Well, after I started the car to move it further into the garage so I could close the garage door, the sound went away. So I'm puzzled as to what that sound may have been because it was a different type of sound than the gas vapor pump doing its thing.
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Welp, I think I may have found the problem. There was a TSB released on this in March 1997. This makes me a little angry though because the original owner complained specifically about this noise to an Authorized Lexus Dealer who just excused it off saying they could not pinpoint it or that it was a "normal cooling off sound" (3 times he complained, I still have the paper work to show it). This was in November 1997, WELL AFTER the TSB was released. The problem was never fixed. Now 14 years later I see this TSB. Is there a way to show this TSB to Lexus and have them replace the part? Because the part alone seems to cost $250.


EG003-97
Title:
EVAP CHARCOAL CANISTER NOISE
Models:
'96 LS 400
DATE:
March 7, 1997
Introduction
In some cases 1996 LS 400s may exhibit a slight "buzzing" noise, heard from the EVAP charcoal canister, when the engine is turned off after driving. To minimize this noise, an air chamber has been added to the charcoal canister assembly on 1997 models.
Affected Vehicles
^ 1996 model year LS 400 (UFC20).

Parts Information

Previous Part Number 77740-50042 New Part Number 77740-50043 (although I've read online that this part has also been replaced by 77740-50044)

NOTE: Previous part is fully interchangeable with current part.

Repair Procedure



Replace the Charcoal Canister Assembly on affected vehicles which exhibit this condition.


FWIW

 

did you pull out your key when shutting the ignition? i suspect it's the HVAC vents or heater control resetting, but i have not heard that on my 97 ever though i never payed attention or my music is too loud .

 

I get the buzzing sound after I have turned the car off and removed the key. You hear it if you sit in the car for a couple of minutes before exiting. I also get a purging sound when I first start the car for the day. It sounds like someone is farting lol.

 

I've not noticed this on our '97. Darn you...if I hear it it will be your fault by making me aware.

 

That's funny, just for kicks when I turned the car off and waited but I didn't hear the sound. I guess I didn't wait long enough though.

 

A lot of toyota vehicles purge the ABS system when turning on or turning off the vehicle, its just now days they make the systems ready up and purge while other functions are happening so you don't notice. Like the toyota venza at start up runs the ABS actuator, but locks the vehicles doors at the same time so people don't hear it.

So it could be a number of things, your blend doors for the ac, EVAP like the posting above or even ABS.