I was out at the beach today for the second time - trying to use the Excalibur 1000 in the surf. The first time I went out it worked very well. After about 45 minutes it started to get unstable. I figured that maybe some sand had made its way into the coil cover. I would hear all different tones whenever I moved it through the water It was even worse whenever a wave of water passed over. I went home and sealed the coil cover with silicone. I took it back out today and the same thing happened. Settings: No Discrimination, Auto Sensitivity. It works perfectly in wet sand and in water that isn't moving. Is this normal? Is there something I can do? Sould I use it without the coil cover? Thanks for your help.