With your gain to low its going to "hunt" and to high it's going to scare the ever living pooh out of you by twitching 90 degrees, the wag of death.
Wags can come from anywhere. First ensure your mechanical stuff is working correctly. Push rod is not binding, servo is still good with little to no slop in the gears. Ensure your pitch slider is running smooth and no binding. Check your bearings in the blade grips, make sure they are assembled correctly and no binding or notchiness. Is the ball link set to the right hole on the servo arm (could have to much mechanical advantage). Make sure your flying a flat or small V curve and no governor. A governor can cause tail issues that can't be tuned out unless you tune the governor.
If that "echo" comes when doing hard tail movements like turning at high speed I would look at your P and I gains. If the echo is from normal flying then your gain maybe to high for your setup, consider dropping a half to whole percent.
As for what is to much or to little: that will be determined by your heli and your flying. We can give you a base starting point but its going to be whatever she wants to fly at. Start at the high end of lets say 60 and work your way down little by little till the tail stops wagging.