Engine compartment noise.

©hester

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#1
Make
Nissan
Model
Altima
Year
2004
Miles
175000
Engine
3.5
This noise occurs right after the vehicle is turned off. Noise can be duplicated by cycling key on key off. It has a rhythm similar to that of a windshield washer pump and the tone of a step motor/valve. It seems to emanate from the middle/bottom of engine and cycles 3 to 4 times b4 it stops. It's like something is trying to reset or recycle itself. No drivability issues. No check engine light.

Has anyone come across anything like this?
 
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©hester

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#2
100 people and not even a hint? I was able to get under the car today. It sounds like the noise is internal to the engine. Hard to pin point with or without a stethoscope. Any clue what could cycling inside the engine? It's very reminiscent of a cycling step motor/

Any WAGs out there?
 

billr

wrench
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#3
Well, I didn't answer before because a WAG is all I had to offer; was hoping you could get something better. So...

It looks like that has an electric "drive-by-wire" throttle, and I suspect it is a (hefty) stepper that operates it that you are hearing. Yeah, you seem to be hearing it someplace else, by noises are notoriously hard to locate or identify accurately.

The only other things I can think of with little motors that come on briefly at key-on are HVAC blend doors, trans actuators, active suspension, seat belts, and fuel pumps; maybe ABS too?. Those sources are just as far from the "engine insides" as the TB. Does this engine have "variable" intake runners? Maybe those are electric actuated. VVT might be another possibility, but I have only heard of VVT that is actuated by oil pressure, never a motor.

See? Lots of guessing!
 

©hester

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#4
Hey Bill. Thanks for the response. It is a drive by system. The throttle body is a convenient location to get an ear on for a listen. However, with an ear right next to it, the noise seems to emit from somewhere other to where I'm listening. I will remove the snorkel to verify any moment of the throttle plates.

Although this noise will occur with the key is turned on, it was first noticed and is predominant after the key is turned off. I thought of a trans solenoid/actuator noise, but after being under the car, it seems louder under the oil pan. Electric oil pump? I don't one of the those exits.

Not sure on variable intake runners. I don't have any experience with Altimas. Was that a thing in 2004? I will look at the ABS. WT?

Again thanks. I'll let you know what I find.
 

©hester

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#7
Thanks Dan. Point taken. Never too old to learn something. I saw that when I was rooting around, but dismissed it when I saw the vacuum hose.