I'm shooting a 50# Martin Vision with cedar arrows. I usually shoot only two arrows at a time because my son and I shoot together and don't want to get the target too crowded. I have noticed one of my cedar arrows has suddenly started to porpoise while on it's way to the target. I marked the knock with a sharpie so I could tell this one apart. The other arrows don't do it and this one didn't or at least I didn't notice it until a few days ago.
 Anyone ever have an arrow change it's personality like this?

    Rusty <><

Maybe it's no longer straight.  Maybe it's cracked.

I checked for straightness and it looks to be fine. There is however checking of the finish. I'll have to examine much more closely for cracks.

     Rusty <><

Rusty:
Hold the arrow by the nock and rap the arrow against your knee cap, a crack will usually rattle. Also check the nock to see if its loose, or is it tight on the string.
Bob