I think that your system is suffering from what is called a ground loop. Here's how it works.
The earth is a round ball spinning in space. it is made up of conductive and non-conductive materials. It is also surrounded by a huge magnetic field. If you look up magnetism and electricity you will find that they are basically kissing cousins. That is they are both the flow or vibrations of electrons in a fixed path. Therefore we can create electricity using magnets and we can make magnets using electricity.
So what does that have to do with your problem.... Well, if we took a ground rod (solid copper) and we drove it into the ground in say Iowa, we would probably hit a very solid ground. This is because of the high mineral and moisture content of the soil. This solid ground would mean that we would have a depletion of electrons in the ground. This is the basic start for current flow.
Now, I take a similar ground rod and drive it into the earth in Texas. Here the ground is very sandy and dry. Consequently, even though I would have an earth ground, it would not be as good as the one in Iowa. Therefore I would have an excess of electrons in the ground as compared to Iowa's ground rod.
Now, let's run a wire from the ground rod in Iowa to Texas. Without connecting the wire to the rod in Texas, is it possible that if I hooked up a meter that I could see an electrical current? Absolutely. This is because of the electrical potential difference between the ground in Iowa and the ground in Texas. This is also referred to as a Ground Fault. As soon as I connect the wire from Iowa to the rod in Texas, it would become a loop... That is the electrons flow up the rod in Texas, across the wire into the rod in Iowa, down into the earth and back to Texas via the earth. This is Ground Loop. The loop is between Texas and Iowa.
The last thing to understand is that this phenomena can happen at any distance from a few inches to thousands of miles. They can come and go according to moisture, mineral content of the earth, and magnetic in fluxion from sun spots and other such things. In other words, grounds loops are very unpredictable. Here today and gone tomorrow or visa versa.
Now back to your problem. When you view the image on your monitor and you are at the camera, the monitor and camera are both at the same ground potential. therefore, your image is clean. When you move your monitor into the other building however you have created a ground loop. The earth ground at the camera is of a different potential than that one at the monitor and you end up with current flow on the shield of the coaxial cable.
There are several things that you can do to cure this problem.
1. Install a none conductive signal carrier such as fiber optics, microwave, or something of this sort.
2. Install a an active or passive ground loop corrector at the monitor. This is basically going to be a 1:1 bypass transformer or some sort of optic isolator. The objective is to break the shield of the cable to remove the potential current flow. These units run between seventy five and two hundred dollars dependant upon the type and needs of the unit.
What ever you do, do not remove the ground plug on the monitor or remove what ever ground that you have at the camera.... This sets you up for an electrical shock if you touch ground and the monitor or camera at the same time. At any rate, you can get a ground loop corrector (GLC) from any major CCTV distributor or dealer. I hope that this information helps you out. Let me know if there is anything else or if the problem continues and I will do what I can to give you a hand. I am in your service.
