FX Bobcat MkII

This is probably a dumb question, but its driving me crazy. I have had my Bobcat for a couple of months, and love it. But tonight I noticed that when it is NOT cocked, it has a rattle to it when shaken a little (by a little, I'm talking a pretty good shake, butt barrel (like up and down vertically)). It kind of sounds like an un-tentioned spring sliding on a shaft. If you have one of these fine guns, could you please give it a shake and tell me is this is normal? I am hoping they all do this, and I don't have an issue. 

I appreciate you help.