If you have bad mineralization you may have the sensitivity set too high for the conditions.
1. With the MF Concentric on, go outside.
2. Set the sensitivity to 15.
3. Find a piece of ground free of targets.
4. Auto noise cancel with the coil waste high.
5. Auto GB a couple of times over the exact same spot looking for consistency in the GB number +/-2.
6. Tell us what that GB range is. i.e. 16 to 18.
7. Put detector in All Metal AM.
8. Pump the coil up and down over the ground like you were Ground Balancing it, and tell us if the detector is spitting out random tones & numbers with the sensitivity at 15. If it is, begin decreasing sensitivity till it no longer reacts. If it isn't, increase sensitivity till it begins to react, and then back the sensitivity down one number. Tell us what that number is.
9. The relative mineralization can be measured using the following procedure:
http://www.findmall.com/read.php?55,574329,574329#msg-574329
Please take at least three readings in the exact same spot and tell us the range of numbers.
10. If the soil is heavily mineralized then using a DD coil is the best bet, also not having the sensitivity too high is important, I would also use GB Tracking as more than likely the soil is also varying quickly, and I would also turn on Target Stability.
HH
BarnacleBill