buzzing noise coming from behind radio....????

On my early '04, I am getting a tinny/buzzing noise coming from the dash. It sounds like it is coming from the area behind the radio. It happens in a cycle, so I think it must be something that turns on and off automatically anytime the key switch is on; 15-17 seconds it is off/no noise, then it buzzes for 25-27 seconds, then off for 15-17 seconds, then on again for 25-27 seconds....over and over. It happens any time the key is turned on, doesn't matter if I am sitting in the driveway with the engine off and key turned on or if I am rolling down the road.
I can't isolate it any closer. It is not the blower fan, the radio is turned off, the cd player is off. It almost sounds like a plastic against plastic vibration.
Any one have a clue what I should be looking for?

 

Are you sure it is inside and not on the firewall or engine compt.? your truck may have a small vacuum pump on the Pass side engine compt.

 

Raise the hood, turn on the ignition, and quickly walk around to the passenger side and listen for the noise near the passenger side battery. There should be an electric vacuum pump on the inside fender between the battery and the firewall making that buzzing noise. It shouldn't be cycling off and on. It should run for 15-20 seconds after the key is turned on and shut off. Continuously cycling off and on indicates there is a vacuum leak in the system. The electric vacuum pump furnishes vacuum to operate the Cruise Control servo.

Bill

 

Thanks to both of you for this idea. I'll check it out in the morning.

 

Once again, the TDR members come thru! I did as suggested and the buzz is coming from the vacuum pump located near the passenger side battery. Now I have to isolate the leak and fix it. Hopefully it is in one of the lines and not in the pump itself.

 

Side question...could this vacuum pump or servo be the cause of a acting up cruise control?

On a long trip my cruise control will stop working all of a sudden and not work for while. Then all of a sudden I'll try it again and it'll work.

Any ideas?

 

You will need a good scanner to test it

 

I got my vacuum leak fixed today. The "hard" tubing was chafed from rubbing against something under the driverside battery. I didn't find it myself, my shop guys had a machine that injects smoke into these kinds of systems and they found and fixed the problem, muy pronto.

 

That is the line that feeds the cruise servo.

 

I just relocated my coolant reservoir from the front of the engine compartment to the firewall using the factory 2005 coolant tank and bracket for the vacuum pump. If you have a manual transmission, then no pump is used on the 2004-05's. If you have an auto, it does use a pump.

We are both making a blanket statement here. Obviously, you are looking at your truck to base your statement on, and I've purchased the parts proving my statement. Could this be another instance of minor changes throughout a model year?

 

Relocating the coolant tank on a 2004 requires moving the vacuum pump from the stock location next to the battery to just in front of the new tank (from a 2005).

I was noting that I just ordered the new vacuum pump bracket for a 2005 yesterday. It has been stated that the 2005 does not use a vacuum pump, and I'm just saying that at least some of the 2005's must have used them because there is a part number for the specific bracket.

 

I do have a picture of an early 2005 that has a vacuum pump in front of the coolant tank. The picture is what I used as the basis of my parts search.

I hear what your saying, but I do find it interesting that the part listed for the 2004 is identical to what came on my truck (obviously), and we had to order the small secondary bracket that I need, using a part number for a 2005. There are two unique part numbers; one fits a 2004, and the other fits a 2005 (per Dodge). The only other explanation I could see is that the 2004.5 has the relocated coolant tank and vacuum pump.

It's interesting to me that the 2005 coolant tank attaches to the large bracket shown below. That same bracket is mounted on my 2004 (September 2003 build date), but has nothing attached to it. It does, however, have the mounting points for the 2005 coolant tank.

https://www.turbodieselregister.com/attachment.php?attachmentid=100385&stc=1&d=1508651277

Things like this sure used to be easier to figure out.

I don't want to totally hijack this thread, so I'll defer back to the original question about the source of the vibration/noise.

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