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Discussion Starter · #1 ·
Any ideas?? I just got my truck back after being in the shop for two weeks due to trans problems. Went to pick it up today and dealer shows me the new sound she makes: there is a knocking coming from the engine bay somewhere.

It doesn't come on right away though, fast forward to 1:56 in the video. Seems to go away with throttle (at the end of the clip)....

http://www.youtube.com/watch?v=85EM_Imi3cc
 

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If its any help i change the oil pressure switch last week and i got the same noice turns out when i change it a vacum hose thats at the back of the engine bay came loose pluged it up and it whent away.
 

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Trailblazer SS
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WTF sounds like a chopper
 

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It sounds more like an intake or exhaust pulse then a tap or anything metallic. I am still scratching my head on this one. I would recommend that maybe pull the blower and take a look. The engine/blower would have been against the firewall without the transmission in it.
 

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The Lurker
TrailblazerSS 06
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Have you tried the ol screwdriver stethoscope ?
 

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Discussion Starter · #7 ·
Have you tried the ol screwdriver stethoscope ?
actually....yes. I didn't find the exact piece that is causing the noise. I can see a bolt for the headers flange that is visually loose but couldn't get a wrench on it during the heat of the day.

I'll also take a look at the vacuum lines tomorrow. Thanks for the ideas!!!

And Joe, as always, thanks for answering your phone and spending some time with me on the issue.:cheers1:
 

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actually....yes. I didn't find the exact piece that is causing the noise. I can see a bolt for the headers flange that is visually loose but couldn't get a wrench on it during the heat of the day.

I'll also take a look at the vacuum lines tomorrow. Thanks for the ideas!!!

And Joe, as always, thanks for answering your phone and spending some time with me on the issue.:cheers1:
Tighten that exhaust bolt and see what that does. The fact that it needs to be warm before making the sound leads me to believe it is exhaust related.

Always a pleasure my friend!
 

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Just a long shot, but something rattling against something plastic? Perhaps, since you revved the engine and I couldn't hear it at that point, maybe the engine torqued just a bit to stop the rattle, then it settled back and the rattled began again?

How about an upper trans bolt, or something else back there (dipstick tube, etc.)?
 

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moar cowbell
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just throwing out ideas here....

you just got it back from tranny work, could it be that they didn't reattach the fuel line bracket that bolts up to the top of the tranny and its just lying on there rattling?
 

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Discussion Starter · #13 ·
Thanks for the ideas everyone....would this do it?



 

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That is the Evap/Purge Line and yes it pulses vacuum to the gas tank for emissions. Give me a call if you dont know how to hook it back up.
 

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Dude who did this shitty work? Loose header bolt's, unconnected purge lines, what else are you going to find?
 

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The Lurker
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Good find!!!
 

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Discussion Starter · #17 ·
Dude who did this shitty work? Loose header bolt's, unconnected purge lines, what else are you going to find?
Found a midget a few minutes ago....vid to follow:biggrin2:
 

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Discussion Starter · #19 ·
Well, that did it. The problem is gone....the unconnected evap line caused the sound. Thank you to everyone that through ideas out there. Big thanks to Joe for spending so much time with me troubleshooting the issue.
 

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Glad to here it wasn't something major!
 
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