Ace 250

I am new to metal detecting. I researched alot, some of this site, called the website for recommendations and made the decision to buy the Ace 250. I used it for about 2-3 weeks with what I thought were good results. I started to learn the machine somewhat and got somewhat better. I found some silver, wheats and other old finds. Then the machine started acting up a little, beeping and jumping around the scale whether I was scanning the ground or holing up in the air. I seemed to start happening after using it awhile. I happened on three different occasions so I sent the unit back. I got a message today about the unit an and was told that the unit was probably not a good unit for my area in SW Pennsylvania because of the mineralization/coal and such, also probably wasn't my best choice for a machine. Now, I am confused. Is there anyone out there in my areas using a Ace 250 with no problems. Should I be looking at a different machine. I will be calling back tomorrow to let them know what I want to do. Any help or guidance would be greatly appreciated. I am new to the hobby and really like it but I am really confused now. HELP!!!!