It's driving me crazy, one of those annoying things you hear every time but no one in your family seems bothered by it. One of our toilet's will start to run only for a few seconds and then off again. Its like clockwork throughout the day and night. Should I call the plumber or is it one of those easy fixes?
Thanks so much for any advice.

It's one of those easy fixes. Sounds like you're out of adjustment. Water seeping from a faulty flapper would cause the situation that you have. The water leeks past the flapper and lowers the tank level, this kicks the ball cock on to refill the loss. The tanks filled, the flapper's leaking and the whole thing repeats.
Let me show you how to adjust the tank parts. Check the tank water level, it should be at the mark in the tank or 3/8 to 1/2" below the top of the over flow tube. Now look at the flapper, If it has wavey edges on the flat surface or rough spongy spots replace it. The linkage between the flapper and the flush lever should have 1/4" play when the tank is filled. Also, check the small tube coming out of the top of the bakkcock and make sure it's connect to and draining into the white overflow tube. I would check all this out before paying 50$ for a service call and 50$ a hour thereafter. More questions? I'm as close as a click. TOM