Things to cherck immediately:

1. Ensure that the four 3mm grub screws in the mast stopper are secure and holding the main shaft centered. There is a "witness hole" on the top edge of the upper right main frame section to access these screws; one at a time as you rotate the head.

2. Flybar is secure and centered. Paddles are equi-distant from the flybar yoke.

3. Head/blades are balanced.

Things to look at if all the above is okay:

1. Bent feathering spindles (an endemic Concept problem). These are designed to bend at the slightest distess, in order to preserve the plastic head in the event of a blade strike. They MUST be replaced after even the slightest blade bump while flying/landing

2. Loose gear mesh between main and pinion gears.

There are many other potential problem areas, but the information you provided is limited. There are many different kinds of vibrations, and each one is an indicator of a separate problem/problems.

You have a malfunctioning gyro or tail rotor servo. The tail fins, both horizontal and vertical, have no effect on ANYTHING in the hover, except for this: the Concept has a pusher tail rotor, so while the vertical fin may partially damp the effect of a nose-left command in hover, that is the only effect you will see.