Has anybody done any changes to the system recently? The solenoids do humm,but they dont do it loudly unless there is a problem. I think you should get a voltage tester,or a multimeter.An autoranging multimeter isnt much more price wise,but you can test every aspect of your system.
Take a look on the terminal inside the clock.The terminal is where all the colored wires go inside the controller. You will see where all the wires line up and are numbered 1-6.Before zone 1 is the common or C slot,white is probably in that terminal. Before the C terminal is, P/MV or pump master valve. Check to see if there is a wire inside that terminal. If you are not sure if there is a wire in that terminal,shut the clock OFF,and then go turn on a valve manually out in the field. This will tell you if you have a master valve. If the zone turns on manually out in the field when you open bleeder or solenoid,you DO NOT have a master valve. If when the clock is OFF, and you manually bleed on a valve out in the field,and it DOES NOT water. you DO HAVE a master valve.
I assume if you just had work done on your system,you would start by saying i just had work done,and now the zones are not working right,but we need to know for sure,if no one including you has touched your system in 5 years. Then it is almost certainly the clock sending stray voltage. This is where the hopfully MULTIMETER or voltmeter,comes into play. Turn zone 1 on at the clock,then with either lead or (black and red wire on the tester) it doesnt matter which lead goes where. For clarity i will just say, put RED on the COMMON or C terminal in clock,and then BLACK on zone 1. Check your reading,it should be apx 24 volts. Now with zone 1 still on, move only the BLACK lead of tester onto zone 2, ( RED always stays on COMMON while testing ). 2 should have like .006 volts or hardly anything.
Now the TRUE TEST after you check voltage on zone 2 when zone 1 is on.Now you want to turn zone 2 on at the clock, With RED on COMMON terminal,put BLACK onto zone 1,check reading. With zone 2 on,zone 1 should not read any significant voltage. If it does,you need to put zone 1's wire into another free terminal if you have one available. or get a new clock all together.
If you do get a multimeter, set it to OHMS, it looks like an upside C, now with RED on COMMON, put BLACK on each zone wire, one at a time and check the reading,if most valves are say 35,and then one is 200,thats a problem And the solenoid needs to be replaced. ONLY TEST OHMS WITH ZONES OFF AT CLOCK,METER SUPPLIES ITS OWN VOLTAGE FOR OHMS.
We need all these questions answered,voltage tested,and voltage results in order to help more,We do this every day, if we were there we could find the problem 99% of the time in 2 minutes or less with a multimeter. unfortuantely were not there, what we have told you is the problem most of the time. try this stuff and let us know the results.