My 250 will do the same if the sensitivty is set a little high and there is either A) wet sand within 3"-4" down or B) if I am crossing over the wet/dry line. Another Garrett user suggested that crossing over from wet to dry and back again confuses the machine as it has to readjust too often, thus giving false signals. I'm not terribly familiar with your machine, but if there is any type of sensitivty setting bring it way down, then increase it slowly. When it starts giving you the chirps, bring it back down one bar. And for the B), stay on either wet or dry to keep the conditions constant for the machine.
Good luck and HH.