It sure sounds like you have a bad coil. When you get a new coil, do one thing for me. When you hunt, slow down and really go slow, I just cannot stress this enough with fbs and multi iQ machines. Also if you are digging a lot of trash try switching to a high trash/conductive mode, also make sure you do not have the Fe line too low on your disc pattern. Just remember in high trash the Co/fe will be different than say Ferrous coin/combined type setup. I have one mode on my user button so i can hunt in one and switch to the other to check targets. I also noise cancel on a clean spot of ground, Target trace can really help too if you have it turned on. I dug a merc and a buffalo a few days ago in a high trash area with my 6 inch coil , both were over 7 inches deep. Nox is my favorite machine but I won't sell my CTX or Etrac because they come in real handy in certain situations that are trash specific. I agree with IDX the CTX is a great machine and since you already have it, i think a new coil will really help with your satisfaction with the machine.