Next time you see Mr. Sheriff, ask him if everything is okay. Most cops are good guys, and if he is there because of a complaint, he'll porbably tell you "Off the record". By showing some interest, you'll show him that you are not some lowlife that is causing trouble. You can also then discuss the situation with him, and show him what you have done to minimize noise, and all of the steps you have taken to appease the neighbor. Take him in and show him the car. Turn on the charm and get him on your side. Once he is satisfied, he'll pretty much ignore her calls, if that is why he is there. All cops have to deal with her kind of prissy whiners, and they hate it.
Get that cheap decible meter and take readings whenever her gardeners start making noise. Get a friend to go to the edge of her property and take readings whenever you are working on the car. Log everything. If the readings are reasonable, use them in your defense when the time comes. If you find that your readings really do exceed the guidelines, just keep trying to find a way to get them a little lower.
