Your situation mirrors my experience with the Axiom. I went out and acquired a 11x7 DD coil and the detector was very stable just like the 13x11 DD coil. No mater what adjustments I made to the detector I could not get the 11x7mono coil to settle down or work right. I called up Garrett and talked to a nice lady and explained to her what the detector was doing. She indicated if the detector was working well with the DD coils the mono is more than likely defective. She sent me a new 11x7 mono and I sent the defective coil back. The new coil was a night and day difference. It was very stable similar to the DD coils. By the way I knew a Dan Smith when I was a young fellow in Glendora California. I was curious if you were the same Dan Smith.