Mines been rattling for years.
Rattle started a few years back when the valve got stuck in the bush, which of course is stuck in the end cover as they usually are. I tried to hammer it out, which didn't help, I just started spreading the end. I had to take it into work and get it pressed out. So ever since then there's been a bit of a rattle. It still works fine several years later, and eventually you don't really notice the rattle.