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2002 chevy trailblazer_ls
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Discussion Starter · #1 · (Edited)
OK People, here's one I never seen before....

Today I am driving my TB and I come to a stop light. I'm sitting there waiting for it change and I hear this sound...like someone tapping quickly...starting out louder and then going softer, until you almost can't hear it......

Da-Da-Da-da-da-da-da. Coming from the engine compartment.

Keeps happening pretty regular like every 10-20 seconds. No engine shudder...no decrease in RPM....no Check Engine light....running like a top.

Da-Da-Da-da-da-da-da, Da-Da-Da-da-da-da-da.

Leave the stop light, perfect accel, can't here it anymore. Next time I come to a stop....Da-Da-Da-da-da-da.:)

I know what it is, anyone else care to give a guess?
 

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OK, I'll take this case. Differential diagnosis, team?
How many guesses until the patient dies, Cuddy?

Has to be something you can see on a visual inspection, so no need for lab tests or an MRI. Can't be a drivetrain related issue, at a stop light.

1) Delaminating/shredding serpentine belt?
2) Loose plastic parts, like on the air filter to throttle body?
3) Wire harness cover material whapping into the fan or shroud area?
4) Paper/plastic bag on the front of the radiator, whapping in time with the fan blades going past?
 

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Discussion Starter · #3 ·
OK, I'll take this case. Differential diagnosis, team?
How many guesses until the patient dies, Cuddy?

Has to be something you can see on a visual inspection, so no need for lab tests or an MRI. Can't be a drivetrain related issue, at a stop light.

1) Delaminating/shredding serpentine belt?
2) Loose plastic parts, like on the air filter to throttle body?
3) Wire harness cover material whapping into the fan or shroud area?
4) Paper/plastic bag on the front of the radiator, whapping in time with the fan blades going past?
All Good guesses! But nope.;)
 

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Discussion Starter · #4 ·
I "fixed" it with the flip of one switch. No more noise.....until I flip that switch again.
 

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I would guess that the bearing in the water pump is worn and the fan blade is wobbling. That is what happened to me 3 months ago.
 

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Discussion Starter · #6 · (Edited)
I would guess that the bearing in the water pump is worn and the fan blade is wobbling. That is what happened to me 3 months ago.
I replaced the Fan Clutch, Harness, Water pump and transmission cooler lines 3,800 miles ago.

But good guess. If I didn't know I replaced those items, I would have guessed the same.
 

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I'm going to assume it's a switch you would normally want to be on, and something is operating incorrectly that makes the noise? If it was a switch you would normally have off that accidentally got turned on, I still haven't guessed the issue. If it's a switch for aftermarket equipment you haven't mentioned, that's not a fair quiz. :no:

Also going to assume it is a on/off kind of switch, not a window being down 1/8" or the sunroof being slightly open.

AC control switch, to turn it off since something is whapping onto one of the AC tubes?
 

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Discussion Starter · #9 ·
OK. So, I have to get to bed here pretty quick.

I open the hood and I start looking around. I don't see much wrong. But I still hear this noise. I get myself a bright light and I REALLY start to watch every component each time the noise sounds.

I see that everytime the noise happens, my A/C clutch turns a little bit. So I go into the truck and I turn on my A/C. I go out and look at the clutch and it is spinning around fine. The noise doesn't happen anymore. I go back in and turn the A/C off. A few seconds later, I hear the noise start up again.

It's the bearings in the A/C Compressor clutch assembly. Apparently they have gotten rough enough so that every so often, the bearings catch the outer race as the belt turns it and spins the clutch when it's not supposed to turn. Everytime I hear the noise, the clutch grabs a little bit and turns a little.

Compressor looks like a bear to change. Expensive little bugger too. Not looking forward to it.:(

Good guess roadie...you get to change it!
 

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It's your lucky day. Somebody just posted a how-to with pictures of replacing that bearing, and the compressor itself can stay. Using the search function is left as an exercise for the student. :yes:

Very interesting report. Thanks for the challenge, even if I never would have guessed that exact scenario.
 

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holy crap, finally an answer, I'm gonna have to look into this tomorrow to see if this is my bugger too, It's so annoying at stops with that infernal rattle.

So with the AC on it goes away? :undecided
 

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was your air conditioner on at the time of the stop light? if it was off that would eliminate another variable of what it might be
:bonk:
 

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Did you miss post #9? The AC switch being OFF was the cause of the noise, as the bad bearing rotated the clutch when it shouldn't have been moving. Turning the AC ON made the noise go away.

The problem is diagnosed.
 
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