I have a '94 w202 that is making a 5-ish second sustained beep from the dash apparently at random. It's not the parking brake or door noises, just a high pitched continuous tone. no dash lights appear.
It's not the brake fluid sensor (had that before. Different beep.) doesn't seem to be affected by throttle or brake inputs, or speed, etc. just beeps maybe twice an hour when driving.

I'll have to dig out the scanner and see what comes up.

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'94 c280 286000KMs