Axiom False Signals, Or Something Else?

[Az_Ed]

I've been volunteering to do a lot of metal detecting on an archaeology search effort in southern Arizona.  I use the Garrett Axiom with the 16" mono coil.  We dig everything detected.   Last Monday I found a copper shoelace aglet likely from the Francisco Vazquez de Coronado expedition of 1540...the find of the day.   The Axiom has been very effective with the project.  Yesterday I hit a signal I am thinking was false.  The terrain was mostly sandy dry soil in a lower river valley area.  I had what appeared to be a broad clear signal with a lowering tone that was sounded deep.  Double checking with a Minelab GPX-6000 using a 14" DD coil showed no response at all.  I don't know what the Minelab setting were.  On the Axiom I run Fine, manual ground balance was 52/28-51/29, medium speed and 4 on the sensitivity.  The signal appeared real to me, but likely deep.  Digging down about 2' showed the signal as still real on the Axiom, but nothing on the GPX.   The edge of the 16" coil on the Axiom clearly showed a signal when it was entered into the hole at an angle.  The only wild card was a 5" diameter Mesquite tree root at the ground surface on the upper edge of the hole.  I attempted to ground balance with the coil in the hole but it came up with nonsense numbers.  It may be that the tree root was creating the signal, especially when the edge of the 16" mono was near it.  I did not dig deeper due to lack of a good shovel.  I'm still thinking that there may be a deep target not yet reached.  I've found a 2"x5" lead ingot with the Axiom easily 2' down when other detectors did not show it.  I've also noticed that the Axiom will false on charcoal in the ground, especially when it is wet.  If anyone has any ideas on this please let me know.  I really need to trust what the detector is telling me.  Are there techniques with the Axiom to determine if a signal is false?  Thanks for any comments, Ed, SaddleBrooke, Az.

[GotAU?]

Moist soil also set mine off in an area that had deep red (iron containing) soils. The only suggestion I can give is scrape the dry surface soil off of a spot adjacent to and as deep as the original hole and test it. If your Axiom doesn’t sound off, then the other hole may have a real target.  Try to ground balance inside the test hole if there’s no target in it and then retest the original hole.

[Az_Ed]

I tried ground balancing in the hole and the Axiom came up with nonsense numbers and was unusable.  I'm still thinking it was a real signal and I need to get a big shovel. 

[Knomad]

What GotAU suggested is a good idea.

I would try settings other than Fine, I know in some locations with especially the 7" DD it can be Over Sensitive to some ground, but any setting but Fine often will work. 

[Nikko]

The Axiom runs hotter than most if not all other PIs.  The 16" DD-FC will find hair thin, beard trimming sized wires of iron and hit them hard.  Don't be afraid to turn the sensitivity down and pulse timing down as well if needed.