Its not a huge problem but its been getting on my nerve's after two years now. When i turn my truck off and the heater/air **** is in the defrost, vent, or a/c, i will get a buzzing noise behind the dash. Turning the air **** to the off position will turn the buzzing off. The noise will only occur when the engine is off.
Just recently i learned that by putting on the four way flashers while the engine is off and the noise is occuring- will stop the buzzing by itself. Turn the for ways back off the buzz comes back. I've traced all of my vacum lines under the dash and have found no lines leaking or disconnected. I still cannot pin-point where it is coming from even after removing the glovebox and ash-tray. I havent been concerned about the four wheel drive being affected becuase it is manual in my truck. Everything else works fine and all of my heater dash ***** work fine . Turn signals work fine . Everything that leads me to thinking its the GEM dead ends there since everything else works fine. I can live with it as i have been doing by turning everthing on the heater air controls to the off position before i shut down the truck so it will not buzz behind the dash, But at the same time im looking for some advise.

 

thats kind of trippy. my truck makes a wierd buzzing noise sometimes when i turn the key to "wait to start" then it goes off when the truck starts. it does it in all settings, ac on/off, defrost, whatever. Its not the worst but kind of annoying. not sure what it is but im hoping its not a vac leak.

 

Just a thought, I used to get radio interferrence from the temp **** being in the extreme hot or cold position, have you tried turning the heat **** while hearing the noise?