I am posting this for informational purposes as I finally fixed the problem.
My tail fin would vibrate intermittently at various headspeeds ever since my maiden flight. I pretty much at one time or another replaced nearly every component trying to figure out the cause.
I finally found it out. While building my N5C TT, I took note that there were some small shims on either side of the tail bevel gear. Well these are not in the manual for the N5C TT or the E5 (nor were the shims included with my E5), so I checked the E7SE manual and found them on page 31: "106-601 6mm Shim." I got to thinking about it- any axial play in the tail output shaft could be translated as intermittent vibrations when the flybarless system makes minute tail corrections, so I said screw-it, and ordered a set. I put them in my E5 and the tail fin vibrations have all but disappeared.
Cool.
