Old feathers can make more noise than new vanes, but normally feathers in good shape don't make as much noise as you think unless they have a radical helical to them. And once you damage a vane they make just as much noise if not more than a feather fletch will.

Weak spined arrows have problems with consistency, and can also waste energy. You will have trouble getting them to group well or tuning them, especially with fixed blades attached. Normally a stiffer spine is not that bad of a thing, they fly pretty well and usually tune ok. However a really stiff spine can be tricky to bare shaft or broad head tune sometimes. Normally the only thing you are giving up with an overly stiff spine is you are shooting an arrow that is heavier than you need. Not always a bad thing either.

I think your fletchings making noise might have more to do with how they are fletched than the spine being off. I have shot pretty weak arrows with feathers and didn't notice they made any more noise than usual. You might also have some sort of contact issue.

Paul