Canuck: It doesn't sound like a NodaMatic transmission problem; usually if you check the elastomerics carefully on DI and preflight you can catch problems before they get bad enough to cause inflight vibes.
You might take a close look at the "elevator" at the back of the horizontal stabilizer. There are small bearings at each end hinge point. Make sure these bearings are free, not sticking. I've seen them get hung up, then "let go" a bit causing the elevator to impart a (very slight) pitching moment in flight.