One motor possibly bad?

[Sledge]

I have one motor that when spun by hand (without the props) makes a rattling sound....it still flies okay, but I think perhaps the bearings might be bad. Should I swap out that motor?

 

[N017RW]

Well if it sounds different than the rest than at least an inspection is in order.

Mounting.
Something rubbing.
You may just have some foreign material in there.