Welcome to Coffee Snobs.
Ive sold my Sunbeam grinder so cant look at one now, but from memory if the top burr isnt positioned correctly you will have that problem.
I know it might sound dumb but did you line up the marks when putting it back together?
Also, did you notice if it has any washers under the bottom burr?
If you have the hopper off you should be able to see the bottom burr rise (or is that top burr lower?) i.e. gap get smaller, as you move the dial from 25 down to 0.