High freq. vibration from the engine causes fuel foaming because it's so close to the tank. It could come from the engine itself, the fan, clutch or start shaft that doesn't use a sprag. The tail blades spin very fast too but usually won't transmit the vibs back up the tail so much. Anything on the main shaft (head, blades, paddles etc.) will cause more of a visible shake, but not fuel foaming.
Sometimes on a new heli, the clutch liner can have a varying thickness letting the shoe sling out by different amounts causing an imbalance. As it seats-in, this will true itself or you can 'turn' the liner in a small lathe.
For best results, the fan and clutch should be balanced and then checked for 'run-out' to less than .002 in. (.05mm) after mounted to the engine. Most of these components are machined to tight specs and are self centering when mounted so that they run true enough to not cause a problem, but just because it runs 'true', doesn't mean it's balanced.
Being you still have a foaming problem, I would do both.
A good prop balancer or a high point balancer works good but be sure that the part is spinning 'true' in the cones before you start removing material. Always mark the heavy side and rotate it in the cones to see that the mark falls to the bottom repeatedly.
Be sure the clutch shoe gaps are equal and parallel before you check it.
Hope this helps...Good luck!!


Kirk