W211 noise when car is off

[Henkka]

My 2003 W211 is making a weird ”humming” noise that’s coming from the passenger side engine bay, somewhere around the front. Not the SBC pump as it doesn’t vibrate or give off any heat.

It started yesterday when I opened the drivers door after the car had been off for an hour or so. It kept going until this morning. I drove to work, and shut down the car, and the noise kept going. I started the car and let it run for about ten minutes, and the noise was gone.

I went outside to check after a couple of hours and the noise had started again.

 

[ajlsl600]

Sounds like something not going to sleep. Find some means th read any battery drain. Get codes read go from there

 

[Henkka]

I took the stationary heater 25 fuse out and the noise stopped.