I have a new in the original box F455N20 collins filter
(from R390A) that I got at a hamfest many years ago
and stored it away for a 'future project'.

I dug it out recently and was examining it when I noticed
that as I rotated it in my hand I could feel something
inside shifting back and forth. I never noticed this
before (the filter was NEVER dropped in my care and
has remained packed in the original packing material
all this time). Is this normal for this type of filter
or might the unit be defective?