Hey guys first post on here. Noticed the car started making a loud constant beep noise from the interior. Seems to be coming from behind the dash on the drivers side. Sometimes it persists even after I shut it off and stays on for hours sometimes. A buddy of mine told me it could be brake fluid but that seems fine. CEL is from o2 sensors. Videos are attached. Any ideas of what this could be? It’s driving me absolutely crazy.

 

I've heard that before in a 2GS when the brake booster was going bad. Wonder if it's similar on the LS400.

 

That's really interesting, Thomas. OP, how do your brakes feel at the moment? Does it make any sort of hissing sound when you press down on it?

Also, when does the sound happen? Does it begin after starting the car, and continue after shutting it off?

To me, it sounds electronic, but I can't say for certain. Your aftermarket voltmeter in the coin tray is interesting. How is that wired up? I also see you have an aftermarket headunit

Do you have any other aftermarket modules installed on your car, like an aftermarket alarm, push button start, dash cam, etc?

I'd probably start by disconnecting each aftermarket item first, and see if the sound stops. For your radio, I'd remove the radio fuse temporarily under the dash.

 

Here's an example:


Slightly different in pitch, but similar.

 

It does sounds like a whistle. It might be the brake booster leaking vacuum. Next time it makes the sound, get under the hood and disconnect the vacuum hose running to the booster. If the noise stops, you've at least isolated the source.

 

Hey brother, my brakes feel exactly the same as when I first got the car 3 years ago and they don’t make any hissing sounds or noises. It begins when I start the car but it’s weird because sometimes it’ll go days without doing it. But the noise continues after I turn the car off completely and even close the door. The gauge in the coin tray is a temp gauge since the one on my cluster took a ****. No aftermarket upgrades other than that gauge and my radio. To me it sounds electronic as well.

 

Definitely sounds similar and like you said has a different pitch. Only thing that concerns me is that when he turned off the ignition it stopped automatically. Mine stays on for hours so it makes me wonder if it’s actually the brake booster or if it’s something electronic.

 

Just finished doing that and the noise persists. Thank you for the suggestion anyways though.