do you have the air line hooked uyp, if so, disconnect it, if not, it may have some air trapped inside that did not work itself out yet, i had this problem wiht my 402 for a couple of weeks, then someone posted to unplug it and turn it upside down in the tank, a couple of times, to let the air work out, sounds like it could work, but mine finally stabilized and stopped itself
HTH