2006 Chevy 5.3 Cooling System

Hey Guys,
I have a question about a noise that I here coming from my 2006 Chevy Silverado 5.3 liter. When sitting at a light or in park idling I occasionally here a sort of bump. bump noise coming from either under the
truck or dash. At least that's where it sounds like it's coming from while seated in the truck.
What I'm wondering is can there be air in the cooling system that I'm hearing burping it's self through the system at idle? It almost sounds like a vacuum vent door popping shut but I don't have climate controlled controls, just the standard sliders for temperature, and I don't notice any change in temperature or in air direction.
When the truck was new I had the dealer replace the thermostat under warranty as the truck would only get to about 170 degrees and was sucking gas out of the tank. I'm wondering could they have not bled the cooling system correctly, and does the 5.3 liter usually require you bleed the cooling system when opened up? The heat is normal, no cold spots, the temperature gauge stays steady at 200 degrees when warmed up. It also does this in summer weather when the heat isn't being used.
Any ideas?
Thanks, Brian
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You might be hearing the A/C bubbling as it runs in some setting and the R134 does not vaporizes well in cold temps and will perculate through as compressor cycles. ----------------- TheSnoMan.com
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I guess that's possible, but I hear it in warmer weather as well.
Brian
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I've heard what you describe coming from my girlfriend's 2006 Tahoe. It also sounds as if it could be coming from under the dash. Her engine is the 4.8L V8, but I'm guessing, based on the fact that you hear it too, that it may just be par for the course on these trucks.
Occasionally, right after putting it in Drive and taking off, I'll hear what sounds like a rubbing, low-pitched squeak. Not sure what that is, but it also appears to come from underneath the dash.
~jp
diablo wrote:

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I hear that same noise as well, at lower RPM, it sounds like air rushing going through a vacuum motor to me. If you give the truck just a little more throttle or let off it goes away. That noise doesn't bother me that much, it's the bump, bump that has me wondering, WTF is that.
Brian
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Distributor bushings tend to make noise when worn. I've heard most describe this as grinding noise, which eventually disapate as things warm up. Not sure if this applies, but its a known source of noise.
Cheers
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