Pioneer CDJ-700S Turntable "ar play" Questions

What causes the speed to change from 33 rpm to 45 rpm while playing Probably a sliping belt,. I had that problem with an Acoustic Reasearch AR-1

CDJ-700S, IT IS NOT CUEING ON-DEMAND WITH SOME CDs, IT WILL AT RANDOM FAST FOWARD ON SOME TRACKS. SOME CDs IT WILL NOT START PLAYING FOR ABOUT 1-2 MIN. THIS ISSUE BEGAN ABOUT A MONTH AGO. I TRIED TO ...