Question
My situation is very similar to the one on your website.  When my system changes zones the pipes inside cavatate really loud (copper).  It can be from zone 1-2 or 2-3( I have 5 zones on city water).  It seems to be random.  It however does not on the last zone.  This started this year after Ithe bathroom was remodled and i fixed a leak in the part that you hook up the compressor to when you blow out the lines.  If I have a faucet on and the zone changes, the water is sucked out of the faucet untill the zone is fully operational.  The irrigation is on a timer in my garage.  No more than 6 fixed heads on one zone.  My front yard is maybe 15 feet lower than my back yard.  My house is roughly 15 years old.  My backflow is tested every year and has passed each time.  The city came out and checked my pressure and said it is normal.  I cannot find the most recent one but the one prior to was on 9-28-05 and the backflow tested at 88psi.  I don't know if that psi helps or not.  I too have spoke with every big dog in my area and the reasons I got where as follows:
Too much pressure
not enough pressure
faulty  or dirty valves
too much water demand
air in the lines
let me call you back
thats a good one
Please, any advice would help.  Thank you very much  

Answer
Jake,
 OK, I love a challenge and you gave me some vital info but perhaps not enough.

What kind of valves do you have, do you know?? Toro, Rainbird etc.../?????]
By cavatate do you mean rattle??
For starters Try this find a valve that will shut off the sprinkler system. with the system running slowly close the valve 1/4 way and see if the pipes still do it. Also see if the systems still looks like it has enough water to work. 88 psi is a little high, but not that bad. If it fixes it then it is too much flow if not that eliminates that and it didnt cost you nothing. How old is the sytem, JIM