You have to answer a few questions first. Are you close to magnetic interference? Power lines? Radio or cell towers? What type of detector are you using? If it is going off, try to lower the sensitivity. Your area is usually OK for detecting. It is usually black sand, and hot rocks that make a detector go wild. We just need more information from you to get an idea. I have a Teknetics T2 SE, which is super sensitive. It hates power lines, but can find a piece of bird shot at 8 inches. My Whites on the other hand is a little less sensitive to that type of interference, but will not go as deep. Explain your issues with the detector pertaining to your soil. I hope you get some answers on here my friend. There are a lot of very knowledgeable people on here. And also a lot who are probably good with your brand of detector.
You can get a simple soil test at your local county extension for like 6 bucks. Simple as in basic minerals, nothing fancy. Acidic, alkaline and maybe some trace minerals. Give you an idea anyhow what your soil type may be.
Or try the geology dept at a local community college. They may be able to give you a short answer.