the high concentration of black dirt (i.e. mineralization) overloads the VLF machine. Try turning down you gain. Turn off your discrimination and go all metal. The trash level at the surf line is usually minimal. So dig everything. Make your next machine a pulse induction detector. This type of detector will cancel out the scramble signals from the mineralization.
Could be there are 6 chests of gold about 5' deep. You might want to dig down a bit and see if the signal get louder the deeper you go. Of course it could also be a steel belted radial tire like the one I found at about 4' deep on the beach where I hunt. LOL Good luck!
Just had that happen to mine, its the coil the V3 came out in 2009 and when I first got it,worked great, then after a while I got some falseing here and there. Only had about two months of hunting on the coil
and it still looks bran new, took it to a whites dealer and we put a new coil on it and its back to normal, works great. Great machine, I think the first DD coils had issues. Good luck ,hope you have a whites dealer near you.
Forgot to mention the best part, The whites guy gave me the coil free when I told him how much time i had on the coil.