I found the source (I think). The top has to be raised and lowered manually as you instructed. When locking the tonneau cover I hear a click but can still raise it by hand (after hearing the click). And I don't want to force it. So it is not locking.And thus the beeping.
Do I have to disassemble the locking mechanism and try to find out why or does that part have to be repalced?
Thank you! I truly appreciate your help.