I was using the sport in fresh water lake with the 10" coil, tried to use the coins and jewelry program and raising the coil up and down through the water created lots of chatter, very unstable. Sensitivity was 5/6. All metal seemed to do that as well. The only program that ran stable was the beach program. Is this normal? Or is something up with the machine? This is new, second time using it and again in fresh water. Thanks