burried high tone / out of ground lower tone

[all iron]

Been using the T2SE for a while now and every once in a while i come across an object that sounds off with a high tone... maybe in the 80's or 90's
but once it is out of the ground the target id and tone drops

for example, i dug a very, i mean very small caliber casing at about 6 inches deep ( rang in as if it was going to be a dime or possibly a penny )

This has happened and probably happens with many models of detectors, if not all of them

The big question is why.... what is happening in the ground to do that .... Minerals?
Im sure there are a lot of reasons and was wondering what a few of them are

Thanks everybody / great forum to learn a few things

 

[Elton]

n/t

 

[Digger70pa]

I found a Buffalo nickle in the same hole with old roofing nails that hit in the 80's. Got the nails out & ran my pinpointer in the hole & found the nickle. I was coin shooting with my discrimination at 75. Made me wonder.