Filling speaker Stands?


I have a modest system. Continually look for ways to improve it's performance even to a slight degree. I have read many posts about improvements than can be achieved by filling the hollow spaces of some speaker stands with some type of material....sand, kitty litter, lead shot, and some others. Here are the stands I have......
https://www.sanus.com/en_US/products/speaker-stands/sf26/ 
These stands are of metal construction. There are 2 upright support tubes which are approx. 2" diameter. The stands sit on a carpet floor with spikes. On the top plates are a layer of Sorbothane and PSB Imagine B speakers sit on top of that. The 2 metal supports are attached to the base and top plate with just threaded holes about 1/4 " diameter. Pouring some type of dampening  material would definitely require a funnel.
The reason I ask this question is that, when I thump on each upright post, it rings for several seconds. A dampening fill would minimize this but would filling those posts really benefit the speaker performance to even a small degree given my modest setup? I don't know. Probably, few have experimented with this type of scenario.Thanks for any advice.



jrpnde
Thanks to all offering advice. Seems that everyone has had experiences with all types of fill as to fill material and level of fill. With my current stand configuration I only have 2 options for a fill material.....sand or rice (if the grain size is small enough). Only one 1/4" threaded hole for access. So the tamping down of sand really isn't possible. I do use Sorbothane on the top plate between between it and the speakers. When I purchased these Sanus stands (which weren't very expensive) I did not consider the option to improve performance by filling upright supports to subdue the ringing of those by tapping on them. Maybe, with my setup, it wouldn't make any noticeable improvement. Only after buying the stands did I read about the benefit of filling hollow spaces in all types of stands. Probably, different stands would have been a better option.Thanks to all for offering suggestions.
I suggest you do not use Sorbothane. I have found that it sucks the life out of some components and creates a muffled effect, plus it will leave a residue on the surfaces it comes in contact with. I recommend Herbie's fat dots for isolation between your speakers & the stands.

http://herbiesaudiolab.net/softdots.htm


Another option is cast steel shot if not willing to take precautions. [ dust mask, gloves although the one time exposure level is so low as to be inconsequential  ] Its density it about 75% of lead. Sand is barely 15%

Rice is probably not a good idea as it is organic and not very dense. Rice may damp, but is unlikely to eliminate tube resonance. It's density is half of sand.

Sorbothane has improved everything where used. One must get the right size and duro. As far as marking, who cares about the bottom of the speaker? Sorbothane creates a unit of the stand and loudspeaker. Other materials may not.
My X wife left me and all of her Valium. I used that in the stands to mellow out the sound. Worked as you might have imagined it would. 


soundsrealaudio.....been there. If I had enough valium to fill speaker stands my problem would be much larger than pursuing better sound. By the way...are valium pills smaller that small grain rice?I just want constructive advice.
Good luck with your problems.