Getting a lot of erratic readings lately with my machine , even when I set it at coin range or above. On coin range ,lately it has been picking up lots of trash like old rusty nails,pieces of iron , etc.Lots of signals going in one direction but silent passing back the other direction. Maybe I've just been searching high trash areas and this is normal , not sure. Also , I've been useing my machine at factory settings since I got it about 5 yrs ago - is it time to start tweaking the ground balance adjustment?{ not that I know how to do this}. It is a White's classic 3. Thanks for the help.