Hi DigThenChuck,
I'm sorry you are having problems with your Nox. A lot of good suggestions here so far. I've got hundreds of hours on mine so I'm going to add a few more.
First, I live in the foothills of the Rockies. My detecting areas are on old decomposing granite, volcanic ash and clay, and deep river deposits of mostly iron bearing rocks. Automatically, my Equinox 800 and 600 will detect all of the small (.5gram to .25 gram tiny bird shot sized) particles of naturally occurring iron along with all of the other metallic trace minerals in my soil because of the simultaneous multi frequencies. When I have the detector set up correctly (default Park 1 is the best place to start) and I press the horseshoe button which means that everything is being detected across the whole range of the detector from -9 to 40, I can hear a lot of popping noises like the ground has lots of targets as I sweep my coil even when I know I have cleared all of the human produced garbage. When I press the horseshoe button again most of that noise goes away.
You live in an area of Maryland that has many similar geologic characteristics as where I live. You have coastal river/ocean deposits, then you have decomposing granite, remnants of volcanic activity and gneiss and schist too as you get closer to the hills northwest of you. Even without EMI problems and human trash, you likely have a lot of naturally occurring iron and a variety of differently mineralized soil.
So, first I would go somewhere free of power lines and wi-fi if possible and without a lot of human trash. I would reset your Equinox 800 by holding down the power button for more than 5 seconds. Then I would go to Park 1. The manual says that in difficult soil conditions (which you may have) you should keep your sensitivity around 15 or maybe less. Default Park 1 is 20 which may be too high (I usually have to run mine between 13 and 18, anything higher is not very pleasant) so try 10 to 13 to start. The manual also says that in difficult soil you need to auto noise cancel and ground balance. Try to find and area with as few strong targets as possible. So do the auto noise cancel. If you haven't been ground balancing, hit the settings button again and the second icon will show ground balance. Press and hold the accept/reject button (check mark/x) and pump the coil between 6" and 1" above the ground until you hear some beeps and the number on the screen stabilizes. Hit the pinpoint button to get back to Park 1 and see what it sounds like. If you still have lots of noise with the coil off of the ground or pointing away from you, lower the sensitivity until it settles down and try ground balancing again. Sometimes I have to ground balance over a rock formation or a sidewalk since my soil is so noisy! If it doesn't get quiet you may have a control module or coil problem.
Minelab in Illinois will definitely fix it if there is a problem.
good luck, Jeff