The calculators beeps and displays a message different from the two previous questions. You may have been using the variables in a different directory. If you can't remember which directory you were using, you'll need to check all the directories in your calculator. Refer to chapter 5 in your User's Guide to find out more about directories. Sometimes my HP 48 seems to pause momentarily during a calculation.
Nothing is wrong.
The calculator does system cleanup from time to time to eliminate temporary objects created from normal operation. This cleanup process frees memory for current operations. This happens less often if you make more memory available. The Equation Library uses and creates global variables. Over time, my calculator seems to slow down.