There is a rattling noise after a few years, 5 years in my case. The upshot is to remove the bottom cap and add 2 washers around the center stem. This will push teh whole assembly tighter together.

Concurrently, I also identified where those two plastic pieces go.

There are 6 exterior screw you need to remove AND they are bigger than conventional sizes so they are easy to strip! Use the cheap set (in pic on next page) I bought for $2 to get the right fit.

WHen you get the cap off see the very center screw? Take it out and put on 2 washers (1/2" outside diameter, 1/4" inside diameter). Wy 2 washers and not 1? ! washer is not enough to fill the gap causing the loose fit and therefore the rattling noise.