I have the Sovereign series racks, but was a little confused on how to fill them as well. I had to knock out the caps on top of each stand. I used a threaded rod (bought from a hardware store) and a hammer. I also filled mine with lead shot (from a gun store), the welds weren't closed enough to hold sand. No ringing anymore.
In addition, I bought some sorbothane sheets and cut strips to place the shelves on instead on the rubber feet.
http://scientificsonline.com/Product.asp?pn=3037000&sid=google&cm_mmc=google-_-cpc-_-edmu-_-sorbothanesheets&bhcd2=1167063033
In addition, I bought some sorbothane sheets and cut strips to place the shelves on instead on the rubber feet.
http://scientificsonline.com/Product.asp?pn=3037000&sid=google&cm_mmc=google-_-cpc-_-edmu-_-sorbothanesheets&bhcd2=1167063033