using setinterval to make my ajax call repeatedly not behaving correctly?

using setinterval to make my ajax call repeatedly not behaving correctly?

  1.  function CheckNewImages() {        
  2.          if ($('#hdnNewImageCheckRequired').val() == "True") {
  3.              $('#newImagesAlert').show("slide");
  4.              var data = '{"caseID": "' + $('#hdnCaseID').val() + '", imageCount: "' + $('#hdnImageCount').val() + '"}';           
  5.                          
  6.              $.ajax({
  7.                  type: "POST",
  8.                  url: "<%=GetRoot() %>Teledermatology/loggedin/teledermwhatsnext.aspx/CheckNewImages",
  9.                  data: data,
  10.                  contentType: "application/json; charset=utf-8",
  11.                  dataType: "json",
  12.                  success: function (response) {
  13.                      //ok we need to show an alert to the user,                                                
  14.                      if (response.d.Result == true) {                        
  15.                          $('#hdnNewImageCheckRequired').val('false');
  16.                         
  17.                          //the new images were found
  18.                          $('#newImagesAlert').hide("slide");
  19.                          $('#haveImagesImg').attr('src', '<%=GetRoot() %>teledermatology/images/tick.jpg');
  20.                          $('#checkResultImg').attr('src', '<%=GetRoot() %>teledermatology/images/checkResultImgtick.jpg');
  21.                      }
  22.                      else {
  23.                          //else no new images were found.
  24.                          $('#newImagesAlert').hide("slide");
  25.                          setInterval(CheckNewImages, 10000);                        
  26.                      }
  27.                  },
  28.                  error: function () {
  29.                  }
  30.              });     
I have the function above that gets called on document.ready().

It makes a call to the server and if certain criteria isn't met I return false and then want this function to get called again in 10 seconds so use setInterval.

This isn't behaving properly though, the 10 seconds tends to get smaller until eventually the page is going nuts as the slide effect i have to state the call is being made flashes on and off.

What am I missing?