A bit confused with my AT Pro.

[ThierryA]

This past sunday I decided to go on a hunt at a park not too far from my house. Besides the usual Pull tabs and bottle caps signals, I also got some clad for the first hour, hour and a half. I was about to leave and began making my way back to the car with my coil still close to the ground when I got this high pitch sound with a reading between 87 and 90 at approximately 6''-8'' deep. Went over the spot multiple times and got similar readings. I got very excited and dug and 8'' plug with my Sampson (I love that shovel) in order to try to lift it in the plug and avoid scratching whatever it was I had detected. I placed to plug on the ground and ran the coil over it, moving the plug around so as to not miss anything, but to my surprise, nothing. So, I placed my coil over the hole and............again NOTHING. ARE YOU KIDDING ME?? I had had occasional similar "false signals" in the past and thought it had happened again. But, I didn't give up and put my pinpointer in the hole, and Oh to my surprise, it gave me a signal. Got some more dirt out of the hole and about 1/2'' deep there it was; a good condition, shiny silver Ben Franklin 1954 $1/2. Got really excited but also a bit puzzled. How could my very reliable AT Pro miss this quite obvious target.
Now, as I said earlier it had happened in the past with a much fainter sound but a reading of mid 80's though once the plug was out NOTHING: in the plug nor the hole.
My questions to you experts brethren are the following:
1. Has this ever happened to you?(the fake signals, or the missed coin).
2. How do you explain it?
3. Is there a problem with my detector? (just to let you know, as far as I know the machine works really well and hasn't disappointed me yet).
As always, thanks much for your input.

 

[Maxwedge]

Are your headphone jack and coil jack screwed in snug? If so, you might call Garrett . They are very helpful and great people. Great find. HH-Mark

 

[8720roger]

It could be that wen you dug the plug the coin got turned on edge.it happen to me a couple a times just don't give up until your satisfied it was a false signal.

 

[John-Edmonton]

Yes....it's happened to me. Causes?

-the coin was sitting on edge
-the coin's halo was broken, so the coil now sees a smaller target
-a small piece of rusted iron was on top or beside the coin, which masked the signal

Another way to check the plug or hole is to push and hold the pinpoint button and run the coil over the hole and plug. Pin point mode is in true all metal mode.

 

[Grilled Scallops]

Your ground has mineralization. The plug creates a void in the ground, which in turn creates a low conductive signal that will mask other signals. If the mineralization is high enough in the ground, you can even get a signal from an empty plug. If I remember correctly, back when people used the infinium, signals from voids was a topic discussed a lot. This will happen with any detector, happens many times a hunt to me when I'm deep seeking at the beach. Target seems to have disappeared after the first two scoops, no, it is just way down there and your hole is masking it. It will drive noobs crazy, ever seen a noob put back plugs without recovering anything? More loot for me. HEHE