I have a 1999 Dodge Ram pickup truck. While idling, and probably while running a barley audible sound that repeats-itself regularly comes from the dashboard. The defroster is also not working properly. I have a hunch that the sound has something to do with a vaccum? and is being caused by the malfunction of the defroster?
Sounds like you are on the right track. You have a vacuum leak somewhere, you might have to disassemble part of the dash to locate where it’s coming from.
No, it is not likely that it is being caused by a malfunction of the defroster, rather it is more likely causing the malfunction of the defroster.
On some vehicles the doors that direct the flow of air to heater vents, defroster vents, etc. are operated by vacuum. If the line cracks or comes off it will whistle and the symptoms you see are quite likely. Before randomly tearing the dash apart get a piece of garden hose a couple of feet long (or heater hose or similar), lay in the truck under the dash with the engine running and put one end of the hose to your ear. Then slowly scan around under there with the other end until you hear the whistle the loudest. That should help locate the problem. In my experience the cracked hose was always cracked right at the end where it plugged into something, and cutting about 3/4 inch off the hose and reconnecting it solved the problem. If there’s enough slack.