Could be a couple things-

1st- You likely are a bit underspined- I have a 28.5" Katera (the Vectrix replacement) and even at 65 pounds it likes a 340 class spine- the diff in stored energy between the two is negligible taking into account the draw weight difference.

2nd- Your rest either could not be falling quick enough

OR-

3rd, and I've seen this an issue with the Ripcord and Trophy Taker on certain bows/setups-its bouncing back up and the fletching is it hitting it as it passes. On a bow that has slightly angled downward nock travel like most Hoyts and other C.5 type systems do, this can be a real problem if your arrows are underspined.

Eliminate the possibility of the rest not falling quickly enough, and then go from there.