Left Coast Geek

So when I parked the E350 in my driveway 2 hours ago, I popped the hood so I could check the oil after it sat.

just now, went out there, opened the hood the rest of the way, and checked said oil, AOK as expected.

I was doing a casual visual inspection of things under there, and suddenly from somewhere deep in the engine compartment, I heard this thin faint BZZZZZZZZZZT that lasted maybe 2 seconds. 30 seconds or so later, it did it again, and again in another 30s. huh. now, I had locked the car out of habit when exiting it, and I did have the key fob in my pocket when I popped the hood, I don't know if this is remotely related. the engine compartment was just a little warm, not hot, after sitting 2 hours. the bzzzzzzz sounded like a small electric pump or something, with a sort of faint shrill overtone under the buzz.

DFWdude

Ah, you've discovered the Mercedes-Benz BEE...

OK, trying to be helpful... Does it go away if you lock the car (hood open) and wait an hour for everything to go to sleep?

Left Coast Geek

the car was locked after I unlatched hte hood, but before i opened it, but I did not leave the hood open for an hour

my wife is out of town for 6 weeks, I will be getting really bored, I might actually try that. hah hah. mañana.

BenzV12

I vaguely remember something like this mentioned before . I don't think there's a fault with your car ,it must be the way it's supposed to do but why ? That's something I can't provide a clinching answer sorry

Left Coast Geek

my 1989 Jetta GLi ? I understood just about every single bit of its electronics and stuff. ditto my 1992 Volvo 740 Turbo wagon, and my 1993 300CE (3.2L) convertible.

the mojo that happens with the computer systems in these newer Mercedes is confounding.

juststeve

doesn't take much for mine to make noise when the car is off. buzzing and humming from under the hood while the rear suspension snorts like a horse.

KEY08

Yeah, these cars are just busy all the time. I would lose my mind trying to analyze noises in these cars.

pierrejoliat

None of my old Benz's made noises, other than metal cooling down pings, my '03 S500 flashed the driver's side mirror turn signal on occasion, '07 S550 would "relock" itself when parked like I had pushed the remote lock button and every once in a while my '13 E350 will have the LED in the front passenger door handle on, go figure. But I have noticed the '13 "hums" a few time after it's been off a while, my dealer always said it was purging the fuel lines through the charcoal canister, but I was never sure about that really.

ItalianJoe1

There are pumps and fans that can run for hours after the car is shut down for different things. I wouldn't worry about it.

LILBENZ230

I mentioned this same thing before. My 212 did this with the hood closed and all locked up. I never did figure out what it was, but it never hurt anything.

CaliBenzDriver

yep, mine does that too.
I believe it's the coolant system venting internal pressure but wouldn't be surprised if it was ABS or the brake vacuum booster. Mine gets flat routinely as evidenced when pressing the extra hard brake pedal to enable the start sequence
......
Edits:
high pressure pump depressurizing the common rail....?

ygmn

I have read the LED head lights have little cooler fans or something internal to them...

but as joe stated above I a sure there are other tings making noises after shutdown..
I hope one of them is something pumping coolant or oil thru turbos to keep them cool and extend bearing life.

KEY08

^yes, the LED lights have cooling fans that run after shut down. It is a very distinctive fan whine and not this buzz noise. Locking the car shuts down the fans most of the time.

S. Madman

You all never heard mine. Air bags puff and hiss at me, fuel pumps whine. It all happens when I walk near the car. It's like it's saying: are we going out!! are we going out!!!