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2000 Chevy, 2500, 5.7 It sounds like a broken belt coming from the dash. It does not stay in time with engine rpm's. It comes and goes at any speed from idle to highway speeds. It does not make any difference if the HVAC system is on or off. Just replaced the air blend actuator and found heater core has been leaking which will be replaced next week. Does it make sense to anyone that the leak could somehow be connected to this noise? Chime in please, and thanks.
 

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Yea, Im thinking its in the hvac box somewhere. A stethoscope may be helpful in finding the issue.
 

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Does it change speed it the blower speed is changed?
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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Could it be an actuator slipping? Our '04 Burb had one slipping intermittently that would make a popping noise as it jumped the tooth. This was not tied to the AC being on or off, as it would try to index when the vehicle started, give up, and try again later. Sometimes it would last a minute. Other times it lasted the entire drive.
 

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I have the same noise on my 05 sierra last a good couple minutes then goes away.

Summer time the a/c on the driver side will go to hot turn truck off and on back to cold.

My 2005 sierra does it had a 2000 Pontiac grand pri also did.

Not sure what to change since it was very sporadic.
 

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Discussion Starter #6
The noise comes and goes with fan on or off. With HVAC controls off and actuator laying in floor (disconnected) while I went to pick up the new actuator.......flap, flap, flap whether I"m driving or stopped.
 

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The blower fan is a "squirrel cage" design, there is probably something caught in the fan.
If like mine, it's behind the glove box and should drop straight out
 

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The noise comes and goes with fan on or off. With HVAC controls off and actuator laying in floor (disconnected) while I went to pick up the new actuator.......flap, flap, flap whether I"m driving or stopped.
The HVAC system in these trucks are nuts. I never really noticed how mine acts before I installed electric cooling fans. I tied the relay into the AC clutch switch so that the fans would come on when the AC compressor comes on, along with the temp switch, and a switch on the dash just as a back up. With nothing on ( heat, ac, deforst, ECT. ) the AC compressor comes on out of the blue. This turns on the fans, and thats why I notice the compressor kicking on. IDK if it does that as Im driving, but it happens all the time at idle. It doesnt last long, only a few seconds to a min., but nothing is on. Have you pulled your ac fan, and looked inside the HVAC box. Wont hurt to look inside the box. You can pull the filter while you have it open. Mine had fallen apart more or less. I just discarded it, and Im running without one. They only way to access the filter is to pull the fan.
 

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Here are a bunch of videos on pulling the fan
 

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2000 Chevy, 2500, 5.7 It sounds like a broken belt coming from the dash. It does not stay in time with engine rpm's. It comes and goes at any speed from idle to highway speeds. It does not make any difference if the HVAC system is on or off. Just replaced the air blend actuator and found heater core has been leaking which will be replaced next week. Does it make sense to anyone that the leak could somehow be connected to this noise? Chime in please, and thanks.
There is usually more than one blend actuator. Check and see if you have more maybe a different one is the noise maker.
 

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I have an 04 Silverado with a little over 200K miles and had a number of problems with the HVAC system - blower motor, blower motor resistor and connector, and blend door actuators. There are lots of YouTube videos to show the processes to repair. The blower motor is pretty easy to remove. If I remember it was a single screw and a turn of the motor to remove it. It wouldn't take long to remove it and check it.

There are a couple of blend doors. I have replaced two at different times five or so years ago. They are not all that difficult to change. Some of the screws can be a little hard to get to but the process is pretty straight forward. They used to be 80 or ninety bucks but the price has come down to around 20 the last time I looked on Amazon. Just don't put power to them until you have them installed. The system positions them and if they don't start from the right spot you will have a mess on your hands!

Blower motor resistor connector heated up and melted. It really stank. I've replaced mine and a friends.

These seem like pretty common problems with the Silverado line.
 

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you posted this discussion 2 months ago , and im wondering if you found the source of your problem, i think kenny is correct and something is in air box,so again my question did you find the source
 
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