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Knock, knock, knock (Who's there?)

W

wmorrison65

New member
A few minutes after I start driving (when the engine is cold,) I hear a faint "knock, knock, knock" sound. Always three, same even spacing. Can't tell where it's coming from. I assume since it's consistent that it's something normal, but I'm curious what it is.

'01 GTP
 


if it goes away its kinda normal, its a lifter is loosing pressure when it sits over night. oil change used to stop it on my car. if it started to tap, i knew i was over due for sure lol
 
ScottyDoggs said:
if it goes away its kinda normal, its a lifter is loosing pressure when it sits over night. oil change used to stop it on my car. if it started to tap, i knew i was over due for sure lol
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It doesn't sound like that. It sounds like a solenoid or something it being triggered. There are always exactly three knocks, and they are always spaced exactly apart by the same amount of time regardless of engine RPM.

It's quiet enough that if you had the radio on, and/or were already driving fast enough for engine/road noise, you probably wouldn't hear it.

And I just had an oil change within the past month.
 
I tried recording it this morning, with my phone on the dashboard. I heard it "live," but can't hear it in the recording. Tonight I'll edit the audio file and press the "enhance" button several times. :p

Again, I don't think it's a problem, I'm just curious what it is. Wondering if it's related to some emissions equipment that doesn't "kick in" until the engine has warmed up a little bit.
 


Don't worry, my 05 does it too, so did my 01 Firebird. Pretty sure it's something to do with the evap canister solenoid or something.
 
I used to have a 98 Grand AM that did 3 quick little knocks that sounded like it was coming from the back. Did not have to be certain temp it would do it at a light after driving awhile or sometimes soon after startup.
 


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