Thats because the currant draw increases when you are wiggling those sticks and goes back to idle when you stop wiggling.

As CGR suggested to find out which control may be binding a bit just wiggle them one at a time.

Now to answer your question as to whether or not to "go back to Nicd" you need to tell us what is the battery capacity of your battery, not just the voltage.

These days I only use five cell batterys (6 volt) and for an ordinary forty sized sport plane using a 2.4 system I prefer to use a minimum of about 1600 mah.

John