Those who have been using risers for a while may have discovered the
clack that comes when your busing at the top of the riser wears out.
It makes a clack noise and eventually will warp the aluminum housing.
I repaired this with a bearing kit, it replaces the soft brass
bushings with needles bearings and polished hardened bolts. You get a
much more silent and smooth operation with the kit.
Check it out.
http://www.ethotec.com/products_poweriser.php