that's really weird though, if you have everything balanced you shouldn't have vibs, What I meant to say on my previous post was that common vibrations are eliminated with higher head speeds but that's not your case. Other things that you could check are: broken servo gears, belt tightness, ball links, faulty tail pitch slider, bent motor shaft, motor bearings, loose frame screws, or loose head screws, and maybe loose skids? If you hold the heli can you feel a lot of vibration? nothing else comes to mind. If none of the above are the cause then I guess its safe to fly it, but check everything because you never know when its going to surprise ya[X(]

Cheers!
Rene