hmm would be surprised if it's rust, it's only ever been used on a track a handful of times, never seen road or rain. It's been kept in wrapping for years in a loft. It's got a 531 respray sticker on it so i'll take your word about the sand
An old cycling enthusiast who's best years are now behind him has given me his Mercian Vincitore track frame and like Gavins, there's a strange rattling in the top tube. I'm stumped as to what it is.
haha