Some more info would help. Is the unit new? How old is it? Has the machine run well before and the issue your having just popped up out of the blue? Has the machine been modified? Does it false everywhere or just in the water? What are the settings you're running? Is the machine new to you or are you an experienced user?
Some things to look for that I can think of are.
Check all the connections.
Be sure you're dealing with fresh batteries.
Check your settings, jiggle the knobs some with the machine on I had this problem on a machine I was looking to buy, one of the knobs was jerked up, a quick look thru the manual can help too.
Check the machine at the hunt spot, sometimes household electronics can make a machine nuts.
Look the machine over for any signs of damage
Excal 1000, Excal II, Sovereign GT, CZ-20, Tiger Shark, Tejon, GTI 1500, Surfmaster Pulse, CZ6a, DFX, AT PRO, Fisher 1235, Surf PI Pro, 1280-X, many more because I enjoy learning them. New Garrett Ca
If this problem just started I would first remove the coil cover to clean out the black sand that got in there to cause the trouble.
If that doesn't cure it you might have a bad coil where water got inside, coil wire gone bad, or moisture got inside the box. Even though it is supposed to be waterproof to 25 feet, they can leak if not well greased and sealed when you close them back up. One of the reasons Fisher & Minelab went to separate battery compartments.
You might have to send it back in to Whites as my buddies is doing the same thing and he only does freshwater. Oh yeah, it could also only be your cell phone causing it. Try leaving the cell in the car or turn it off.
More information would help if you explain the conditions of the falsing.....Does it false as soon as you turn it on? Does it false on dry sand, wet sand or in the water? Are you seeing the false in shallow water as waves go over it (common)?
I made the mistake of wearing knee high rubber boots that had steel shanks in the souls. I didn't know it at the time, but finally figured it out. After I Changed in to my shoes, all was fine.
Thanks for all the replies,
sorry for not giving enough info, i have had this machine for five months and got it new.
it has been working ok up until a few weeks ago when it became very erratic and would false mainly on the wet sand after coming out of the water.I think the coil might have some water in it as one of the members have sugested,
i have noticed that the epoxy sealing the coil halves together is poress and is not adheared to both surfaces of the coil in some parts.
Thanks again
terry