Ajax response time inconsistent.

Ajax response time inconsistent.

What I'm doing is creating a div element dynamically when the user clicks on a point in the page.  Once created I create a record in my database table the corresponds to this div element and save information such as the width,height, x coordinate, and y coordinate of the element.  This is done via AJAX accessing my web service.  The weird thing is, I get really fast responses 80% of the time but 20% of the time, its taking a lot longer.  For example, I would get a response after 50-100ms and at times I would get it in 2 seconds +.

What do you think is the source of this problem?