Knocking or tapping sound when car is off

[Deuce of Spades]

About 5 to 10 min after i shut my 96 GSX off it makes a slow, deliberate tapping sound for about 30 sec. Then it gets very rapid, similar like an electric motor or small air compressor, for a few seconds and stops. A minute later it goes thru this cycle again and this goes on for about 20 mins or longer. To make matters more weird sometimes when i go to start the car it will barely idle until I give it gas. And the last time this happened it took about 10 min to start the car.

All of this happens once a week, sometimes less, and i drive it everyday.

Its hard to pinpoint but it seems like is coming from the rear of the engine near the firewall. Not positive though....

 

[jimbob_843]

Check your isc? I know they can click when bad. I would start there first.

 

[Deuce of Spades]

Thanks i will test it but the car doesn't have any on the usual issues associated with the isc going bad. Also this only happens about once a week or less. Other than that the car idles and runs fine every day.

 

[TSi Kid]

Definitely sounds like the ISC

 

[99gst_racer]

My engine does the same thing. I've narrowed it down to the valve springs. I can't explain why they are making the noise, but they definitely are. I can push on the t-belt between the two cam gears and increase the rate in which it ticks for a couple seconds before it stops. I have yet to find anything wrong with any part of the engine, but it's been doing this for 1-2 years with no negative affects.

Try pushing down on the t-belt and see if that affects it on yours.

 

[Junfan]

Is it possible for a lifter to still actuate with the car off? I know sounds like a totally dumb questions just wondered if maybe they are still under hydraulic pressure right when you first turn the car off. I understand that the oil galleys pressurize the lifter and I would assume that maybe you are hearing the pressure being relieved from the lifter.

ISC seems more logical.

 

[Deuce of Spades]

Definitely sounds like the ISC

Thanks, I will check it today at work.

My engine does the same thing. I've narrowed it down to the valve springs. I can't explain why they are making the noise, but they definitely are. I can push on the t-belt between the two cam gears and increase the rate in which it ticks for a couple seconds before it stops. I have yet to find anything wrong with any part of the engine, but it's been doing this for 1-2 years with no negative affects.

Try pushing down on the t-belt and see if that affects it on yours.

I will try it as soon as it makes the noise again. I havent even considered that fact that theinfrequent rough starts might have nothing to do with the sound at all.

 

[99gst_racer]

I know ISC's can make noise when they go bad, but it would need to be powered up to do so, right? I would think that the fact that the engine (and ignition) are OFF when this noise occurs, that would eliminate most electrical devices from the list of possibilities.

 

[Talon IV]

I would poop the hood and see if you can pin point where the noise is coming from if ya can. i know valve springs like to tick or pop when you shut the car down.

 

[black_gst]

My engine does the same thing. I've narrowed it down to the valve springs. I can't explain why they are making the noise, but they definitely are. I can push on the t-belt between the two cam gears and increase the rate in which it ticks for a couple seconds before it stops. I have yet to find anything wrong with any part of the engine, but it's been doing this for 1-2 years with no negative affects.

Try pushing down on the t-belt and see if that affects it on yours.

Interesting, my car does the same thing but I gave up trying to figure out what was making hte noise, ill have to try this.

 

[99gst_racer]

Yeah, mine started doing it after I rebuilt the head with my Kiggly springs and Kelford 272s. It never did it on a stock head. Although I'm not worried about it at all, I'd be interested to learn why it does it.

 

[Deuce of Spades]

Originally I was concerned that it was causing my starting issues. Now I just would like to knpw what it is. I will try to pin point the sound after work. Thanls for the fast replies!

 

[black_gst]

Yeah, mine started doing it after I rebuilt the head with my Kiggly springs and Kelford 272s. It never did it on a stock head. Although I'm not worried about it at all, I'd be interested to learn why it does it.

You know how your exhaust pipes tick and pop after a drive, because they start cooling down. Could the valve springs be doing the same thing?

 

[Junfan]

That sounds way more reasonable that what you are hearing is the spring as it is cooling.

 

[Deuce of Spades]

You know how your exhaust pipes tick and pop after a drive, because they start cooling down. Could the valve springs be doing the same thing?

But the sound is not random its a very set pace then rapid and back and fourth. It sounds like some kind of electric motor.

Its sounds nothing like the ticking of a car cooling down

 

[Deuce of Spades]

If it does it when I get home I will post a video

 

[TSi Kid]

If it does it when I get home I will post a video

By the way you phrased this it makes it seem like it doesn't happen everytime. Is it a consistent event or does it only make the noise occasionally?

 

[Deuce of Spades]

By the way you phrased this it makes it seem like it doesn't happen everytime. Is it a consistent event or does it only make the noise occasionally?

In my original post I stated that this happens about once mabey twice a week.