Strange 1000 Hrtz Electrical Tone After Shutting Down (1 Viewer)

[bamelanc]

Turned key off and immediately heard this tone. This is the second time I’ve noticed it. Same pitch both times. Duration was similar. Had enough time to get phone out and select voice recorder and catch almost 30 seconds of audio. The tone/whistle is a straight up B at 1000 hrtz.

I’ve heard similar sounds like this from old power amplifiers are they power off. Maybe a bad capacitor/resistor/transistor?

I can’t upload the audio or video of the screen recording.

 

[bamelanc]

shot in the dark....perhaps unplug the carb cooler at the motor pig-tail to see if its that?

Would I hear this in the cab? I’ll take a look at it. Thanks.

 

[fyton2v]

This is the noise! Posting for @bamelanc. I'm stumped. It doesn't sound mechanical or something created by pressure or a vacuum. It does, however, sound very much like a test of the emergency broadcast system. Perhaps it's only a test.

The Noise

 

[Pura Vida]

This is the noise! Posting for @bamelanc. I'm stumped. It doesn't sound mechanical or something created by pressure or a vacuum. It does, however, sound very much like a test of the emergency broadcast system. Perhaps it's only a test.

The Noise

What the heck, I didn’t know that was a sound a Land Cruiser could make

 

[1969FJ]

Scam

 

[wimberosa]

From what I'm understanding...that is an AC current sine wave B flat. DC electrical systems shouldn't be producing that. Do you have some aftermarket electrical on your truck? Where's @Engineer8000 .... he would know this tone i'd bet.

 

[bamelanc]

From what I'm understanding...that is an AC current sine wave B flat. DC electrical systems shouldn't be producing that. Do you have some aftermarket electrical on your truck? Where's @Engineer8000 .... he would know this tone i'd bet.

Only way to have AC would be to have an inverter somewhere right? The only electrical component that’s truly aftermarket on the vehicle is the tach.

 

[Engineer8000]

What year is your truck? What engine?

 

[bamelanc]

What year is your truck? What engine?

‘74, 1F. California emissions.

 

[JohnnyC]

Did You try running with the gas cap off and see if it still does it as mentioned in post #14

Did not see a response to that

 

[middlecalf]

@Engineer8000 will be your best bet on helping if this is a possible guilty party but do you have a lot extra things that look electronic hanging off the coil?

 

[sggoat]

Only way to have AC would be to have an inverter somewhere right? The only electrical component that’s truly aftermarket on the vehicle is the tach.

AC sine wave is 60 Hz--not 1000--
The only electrical drain after shut down would be if you have a car cooling fan--and that would not decrease over time as your graph indicates--so
this has to be coming from an air/vac system leak, esp since the graph shown decreases over time-- like the fuel tank cap idea--at least that should eliminate the fuel delivery system(and maybe the vent system)--
Is this truck still smogged?
What about the Cooling system? Do you notice this in the cooler months?(heater valve might be leaking thru as the engine coolant pressure degrades)?(this should be easy check--Startup and get engine to op temp-exercise the heater vlv, then shut down and see if the noise is there--OR--startup to op temp, open the heater valve fully--see if you get the same noise when shutting down) hope this helps----(sure is a weird noise from a cruiser!)

 

[Engineer8000]

It's an electronic 1 kHz tone. I have my suspicions.

 

[wimberosa]

well then its gonna possibly be some magnetic buzzer the PO put on it...and its hiding somewhere. Is there any anti-theft devices that you are aware of?

 

[Engineer8000]

I will check my 74 emissions manual.

 

[B y r o n]

Did you ever find the source of the noise?