1994 Toyota Corolla starter

My 88 year old father drives his Corolla about 4 miles/day. On occasion it will not start. The battery is fine and holds a charge. It is not due to weather. 99% of the time it is fine but on some mornings when you turn the key it makes a chatter. No cranking. When you jump it starts right up. At least two mechanics have failed to locate the problem. Any ideas?

Depends on what you mean by a chatter. If is a chatter with an electrical sound like a weak battery gives and the battery is good then it is either bad cables on connections or the starter is saying good-by.If is a much louder and metallic sound it is a bad tooth or teeth on the flywheel or a cracked flywheel.