I have had y t-rex 450 on the shelf for a while, when I fired it up today and flew it, it started rocking back and forth (nose to tail). It feels like when the gain is too low on the gyro, but instead of going side to side it is rocking nose to tail. Any ideas, I can't think of anything?

Thanks

Check your center of gravity. Is your swash level?

Sounds like somethings loose, yesterday my trex450 was doing some shaking front to back, then the  tail was doing some weird over correction, the belt was loose, tighten up the belt and some frame screws, the shaking front to back stopped and the tail came back to its former glory.  </p>

That also sounds like the oscillation from not enough headspeed.

Thats funny you should say head speed, I have 3 lipos, 3s 1800 25c, and 2 3s2200 30c, the 25c is turning rotor faster than the 30c batts, dont have a way check rotor rpm, I have 8 deg on cycli but the slowest roll rate, Align trex 450sa, 35 align esc, 430 motor, Futaba 401 gyro, metal head. took the carbon blades off, put the wood back on and this helped a little, the 25c batt is 5years and the 30c batts are 2years, need new ones, cell volt are still with in 2 tenths or so, I can hear the motor bog down when I punch the cycl, then the tail acts funny, pull slight neg cycl head speed comes back and then the tail comes back. When I go to filp or roll it starts quick and then slows down even faster.  

yup, that's definitely the headspeed wobble. I've got some 3 year old packs that I use as a warm-up and they make the helicopter wobble horrendously at the end of the flight.