Humming sound after engine is shut down

honda
accord

#1

Lately when I shut the car down I hear this “MmMmmMmMMmMmm…MmMmMmmMmMmmMmM…MMMmMmMmmMmMmM” sound coming from the rear end of the car.



It sounds like a cell phone on vibrate, but i’m pretty sure that’s not what it is. Also it’s not the same sound as the fuel pump running when the ignition is turned on.



Oh, this sound goes away after say, 3 min. My next step is to disconnect the battery to see if it goes away, even though I don’t know what else on this car could be making noise.

Any ideas?


#2

Some Accords have the engine cooling fan run for a bit, open the hood after you shut the engine off and see if that is the source of the noise, it may be normal.


#3

you can pull fuses to narrow down the possible causes. Does the car have a rear antenna that is supposed to lower itself when the radio is off? You might start with the radio fuse.


#4

What Model-Year Is This Honda Accord ? Does It Have Self-Leveling Suspension ? Does The Noise Stop If You Open The Gas Cap ?

CSA


#5

Along the same lines, does your Owner’s Manual have any statements about any evaporative emissions equipment running after the ignition is shut down?

I know that the Owner’s Manual for the Rav-4 makes mention of a noise that can be heard after shutting down the ignition, and it states that this is a normal purge test for the evap system. Is it possible that Honda has a similar mechanism on this mystery vintage Accord?


#6

Wow, I have some Homework to do.

It’s a '99 Accord and the antenna is installed in conjunction with the r. defrost grid. So no power antenna. It’s definitely not the radiator cooling fan either. Let me read up in the owner’s manual and get back to you guys, thanks.


#7

Ok, here’s what I have re: this issue:

Engine cooling fan: Nope
Power antenna: N/A
Self-leveling suspension: ???
Does the noise stop I open the gas cap: YES, actually.
Evaporative Emissions Equipment: The Owner’s manual mentions a system like this that stores fuel vapors some or other in a cylinder after the ignition is turned off, but does not mention any kind of “normal” noises.

What do you think gents?


#8

It’s probably the vent in your gas cap. I have heard this sound a couple of times before on a Jeep Cherokee. I simply smacked the gas cap on a piece of wood and the sound went away. The vent was controlled by a small spring as I recall.