Though I have not done such a test on a rotorcraft, I have gone one step further on a fixed wing aircraft, here:
http://www.lakecentral.com/images/HOWboom1.jpg This testing involved deliberate excitation of the boom at varying frequencies, and observing the natural frequency and self damping following the sudden removal of the excitation. This was done by vibration transducer mounted in a purpose built excitation device, mounted in the very front of the boom. The signals were observed by oscilloscope in the cockpit. The test was repeated in every configutation, and speeds up to 1.1 Vne. I also had to do a comprehensive flight test program on this aircraft with the boom, including spinning it.
I will be testing the same survey boom design on a Hughes 500D next week. Excitation, observation of the frequencies of vibration, or a "rap" test, have not been requested by Transport Canada.
I will, of course, be observing the boom during all phases of flight test for unusual behaviour, and performing more in depth testing if that is found necessary.
If you think I could offer more detailed help, feel free to PM me. I am not, though, a helicopter expert, and have no R44 experience. I have no experience with EASA STC process which I consider positive, or helpful in this regard.
Good luck!
Cheers, Pilot DAR