I thought I might throw this one out just in case someone had a similar issue or has any ideas.

I have this 1954 Raleigh Sports that I inherited from my dad.  It was in pretty bad shape when I got it It sat in a shed for 10 years or so after my dad quit riding it in the 60's until the early 70's when he took it out to ride with us kids, then he lost interest in it again in the late 70's and sat  until this fall when I rescued it once more to clean it up -and maybe ride it a bit for fun.

I'm trying to not replace anything that isn't totally unservicable not so much because of it being a museum piece but because I don't want to spend any more money on it than I absolutely have to.  So far all I've replaced are tires/tubes, brake pads, chain, one brake cable, shifter cable and every ball bearing on the bike except those inside the Sturmey-Archer hub for obvious PITA reasons (they seem fine).

One issue I'm having is after I cleaned up and de-rusted the rims I'm hearing sand or rust particles INSIDE the rim moving around.  The thing sounds like a rolling rain stick when I spin the wheels.

Is this at all common?  I've rebuilt a half dozen bikes and never run into this (although this is the oldest vintage bike I've ever worked on).  Is there an accepted method to getting it out?  The valve stem and spoke nipple holes are in the center portion of the rim where the metal is flat an not hollow.  Can I drill carefully someplace to make a larger hole than the tiny weep holes in the inside of rim that allow water to escape?  Will that weaken the rim too much?  Is there a way to fill the inside of the rim hollow with "great stuff" or other foam filler?

The rims were not in that bad of shape with only minor staining of the chrome here and there that rubbed off with only a scrubbie with a little bit of bar-keeper's friend.  Structurally they seem very strong although I'm not sure about that since the "sand" in the inside might be serious rust.

Any input would be appreciated