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First Post. My wife drives a 2007 SC430. Yesterday, 11/1, she was just sitting at a red light. The radio was not on, the blue tooth was not on and all of a sudden a VERY loud alarm started sounding inside the car. It lasted for about 30 seconds and she thinks it came from the speakers but is not certain. On/off, on/off...everything else with the car was fine, engine did not stall nor were there any warning lights. It has not happened since.
Thank you.

 

Was there anything sitting in the passenger seat? If so, it could have been the seatbelt warning. This happened to me once. I was bringing back lunch for the office and it was just enough weight for it to think someone was sitting in the seat.

 

Another possibility could be the NAV system. If a destination or previously "marked point" was reached, a loud chime sounds. The door to the NAV display does NOT have to be open for the chime to sound. Take a look at your NAV manual for more on this feature.

 

Did your wife grow up in the 60's? I have flashbacks like that all the time.

 

Welcome to CL.
If it was a loud BEEP BEEP it was the low air-pressure warning sound (no TPMS light comes on the dash). Mine freaks out every year when the temperature first drops (this year it happened a couple weeks ago). It lasts about 10 seconds and only happens once a year (my pressure's fine), so I choose to ignore it....

 

When my TPMS goes off (audibly), it's just a chime...like the door is ajar or your seatbelt is not fastened. It's not by an means "loud" or, as the OP described it, "VERY loud".

I think the last person on here who had a problem like that discovered that the previous owner of his/her car had installed a hidden radar detector.

I'm curious where the volume of the nav lady voice is. It's like an OFF - 7 scale.

 

yup when the low pressure alerts there is also a low pressure light on the dash and is more of a "chime" than a loud beep...