Hi... I'm chasing some info on a 4CX400 I have just bought..it "ratles" when inverted...as if something is sliding up and down inside the tube. Is this normal, or do I have a dud? The tube marked rc-36b, which I was told is the military equivalent. I also have a GU34b...it doesn't rattle, but I'm after any data anyone may have on its use at 2 Meters. Thanks in anticipation.... Glenn VK4TZL