Lots of humming/buzzing noises depending on the model and year of the coach. Diesels will have an electric vacuum pump for the in dash AC, Heat and Defrost. Rear view monitors will have a speaker that will buzz when its on. Gas coaches will have an electric brake pump that can stay on and cause a buzzing sound. Lets start with what year and model Winni you have.
2001 Winnebago Adventurer WFG35U