VTI BL series racks are popular for the price, but the hollow posts could use some deadening. I've used lead shot and while it works great to deaden and add mass, you have to be careful lifting the sections. Over time, weight and vibes can loosen the lower threaded spike caps. You lift a section, a cap falls off and you have a real project recovering the spilled shot. That happened to me once. One could try a bead of super glue around the lower caps, but it is a metal cap and a painted tube.
Due to a system change, I sold my old double wide BL 503 bought a BL 404. I came up with this method to deaden the tubes. You have to carefully remove the top caps. VTI suggests inserting a long punch through the spike hole and tapping the top cap off. What you use as a long punch is important as a sharp object can dent the thin top caps. Stay at the outer edge of cap, not the center and slowly work your way around.
Get yourself some 1/2" copper pipe insulation. This material was 1 and 3/8" in diameter, perfect to fit snugly inside the tube. Cut to length and insert the insulation in the tube and re-install the top caps. If you want to add mass, get some plastic pipe and plastic caps. Cut pipe to length, glue a cap on, fill with lead shot and maybe some oil and glue the second cap on. Insert in the center of insulation. I used a chunk of 1/2" copper pipe to illustrate. It would be easier to use plastic versus soldering copper pipe.
I used spray insulation once through the spike hole in bottom of tube without removing the top caps, but you have to be careful of excess application. It will continue to foam out the hole and the sticky residue was difficult to remove from the metal cap. That could stain the metal painted surface if it were to get on it, so be careful if you use the spray insulation method.