wierd

Happened upon this rock a while back but still puzzled as to what it might be. I'm mostly a Native American artifact hunter so you can see why I just had to pick it up lol. Strange shape as if someone made it that way, and if not by some natural means there are 3 scratch/tally marks on the top...

I just bought this machine and the first day I take it out, it starts humming constantly no matter which part of the sand I put it on. It does the same thing in the air. I read the manual and did everything it told me to. Can anyone help me with this please?