If you park the bus after driving in the rain you will have water up on the drums to a greater or lesser extent. The next time you go to go, you will have had some rust build up on the nice and shiny surfaces of the brake drum. The first few applications of the brakes will result in squeaking and squealing until the rust is worn off.
I can remember on Monday mornings I would ride the brakes as lightly as I could to see how far I could go until the brakes didn't squeal any longer. I am sure the people along my route didn't appreciate my scientific experiments before 7:00 AM as much as I did.
Setting off car alarms with the bus exhaust was another Monday morning pleasure.
You have to find pleasure in your work or work ceases to be fun.