Horizon Problem....

[Geo]

Hi.
These days i play a little with the MFD. When i give more gain via a preamlifier (i connect it to the coil) i see problems with horizons. My MFD detects very strong the east- west at a angle of 40...50 degrees. So it is not possible to start detect . If i will decrease the gain more (without preamplifier) then the "horizons" disappearing" but the sensitivity of the MFD is not enough. I have shielded the coil with foil, so i don't know what other to Do.
Any Idea????

Regards