6 zones and 2 are not working

Hey everyone,
I have a 6 zone automatic sprinkler system. I seem to be having a problem with 2 of them not coming on. The zones are on different areas of my lawn, one on the front side, the other on the last zone in the back yard.

I really have no clue on where to even start to look at what the problem may be. Any help would be greatly appreciated.

One other note, I did notice that when I ran a "test" on all the stations, at one point, I heard some "whining" type noise coming from one of the stations areas. Would this have something to do with it?

I don't have a suggestion about the whining sound, but I would suggest you examine the wiring to the electric valves. There are individual hot wires coming from the controller to the valves, one to each. There is a single ground wire that are linked from one valve to the other. I suspect a couple of these has lost contact. Usually these are linked with wire nuts that have silicone fillings to keep them waterproof.