I'd suspect drought or some type of leaf disease like bacterial spot. If the tree produces what you want then don't be concerned.

Mine have been dropping leaves as well. With the current drought my trees are still only a year or two old and since I am only able to water on the weekends they tend to get stressed a little and drop their leaves. My plums and pears have all dropped a few leaves and now that it is getting cooler they are putting new leaves back on.

Thanks for the feedback. All seems to be well with it. We usually leave for vacation for a couple of weeks. Maybe the August heat stresses it.