I appreciate the reply. Not sure it applies in my case. I use a CH Eclipse yoke and have mapped an unused lever to handle rudder trim. And it works quite well. For vertical trim I use the #1 and #2 keys on my keyboard. And they work well also. I will try the #3 and 4 keys for rudder and see if that works as well and if it resolves this issue. As for the issue itself, it seems to occur during straight cruise flight, though I will check on that today to verify. And as I said, it is not a dramatic "shaking" or anything like that. It is rather a slight but noticeable "oscillating" of the nose/tail up and down, perhaps 2 or 3 cycles per second and about .5º of pitch. I will tinker with it further to refine exactly when I observe it and if any adjustments, particularly to pitch access, have an effect. Thanks for the replies.