When I turn on my fan, on the HVAC, there is a noise that kind of sounds like a transformer transforming. Sorta sounds like a door creeking and this only happens when I first turn on the fan. Any ideas on what this could be and how to fix it?

 

might be leaves or other junk falling down from the cowl vent to your fan motor or the fan motor starting to go out. from what you are describing it could be either one.

when you first start the fan it might need a little "warm up" to get all the fan motor lube around the fan motor bearings. if you have "junk" by the motor it migh take a few seconds to have the air pressure build up and keep the "junk" from rubbing on the fan blade. either one can be described as a buzzing sound.