due to some kind of interference, monitor display is "shaking"

There is nothing bizarre on that.

Your problem is related to ground connection. It is called "ground loop".

When you disconnected the ground connection with a 3-2 prong converter, the ground connection was cut and problem goes away. But do did the electrical safety that the ground connection created.

When you added that " ground the bottom of the converter into screw", you re-created the ground connection. No woders that shaking came back.

The most danger with the missing ground connection is the electrocution!

As posted repeatedly, he was trying to fix the problem rather than first identify it. Tomi has correctly noted that John H simply broke something rather than solve his probable magnetic field problem. To remain in denial, he then declares it an electrical problem. He did the first test, saw some critical test data, then immediately concluded the problem solved. He even admits he does not know why the shaking has stopped - and does not care.

Somewhere in a previous post, he even mentioned running a ground wire from the AC wall receptacle screw to cable modem. Just more ground loops to create magnetic fields or other problems. However John H has made it clear that he did not want to solve the problem. Worse - he takes insult when this is explained. John H jumped at every kludge solution until monitor stopped shaking.

Operating with an isolated ground may even cause a cable wire fire inside wall should an internal electrical fault occur in his computer boxes. But apparently since that fire has not yet happened, then it will never happen. Again, this is what happens when one wants the immediate solution rather than first identifying the reason for the problem.

Tomi Holger Engdahl identified but some problems with John H's solution. Somehow this does not matter as long as the monitor stops shaking. Clearly John H knows that running his equipment without a safety ground is sufficient. He immediately blames the safety ground - speculation declared as a fact - without learning why his monitor shakes. He blames building wiring without even knowing anything about the building wiring. It is why accidents don't happen. Failures are directly traceable to humans who just know without first learning why.

This post is not for John H. He is simply the example of why failures happen - sometimes why pe> "John H." writes:

So is that to say it is an electrical problem? if that is the case, why did the electrician who came in and looked find no such issue?:(

I'm sorry, were you having a conversation with someone else? Did you just completely ignore what I had said? I was told it was a magnetic field, so I should move things around. I told you what happened when I did that. I was told it was a grounding issue, and an electrical issue, so I called an electrician in, who said everything as far as grounding and neutral lines was OK. He told me to call the cable people, who again came out, and said it was an electrical issue.

To say I am being stubborn or not listening and looking for some immediate answer, or some quick solution, after having THREE Professionals come out is just blatantly dishonest ... seriously.

It's an apartment ... I am limited in what I can do. The landlady and the electrician both said it was not an electrical issue, therefore I had no other choice as far as that goes other than to try something myself, which I did.

This post IS for you, and you are the example of why people often don't seek help because because they are looked down upon by ivory tower know it alls who really don't know the solution.

The problem you have is an electrical problem in the nature. The problem is within either the electrical distribution of your house and/or how the cable TV is wired to your house.

Maybe this is where problem is with electricians and such:

Ground loops are a mystery to many people. Even college-trained electronic engineers may not know what ground loops actually are. Engineers have either concentrated on power distribution (for the electric company) or on equipment that happens to plug in to the power distribution system. Not much thought has been given to power distribution, equipment and other connections to the equipment as a single entity where ground loops arise. You need a system approach top see this problem. Understand the whole system.

It is very posible to have experts on different fields testing the different parts of the system (all in their expertise field) and make a reasonable judgement that all parts of the system are OK and everyhting should work fine. But when everything is connected toghether, there whole sysem does not work well. And everybody can retest their systems separately and tell that they are OK, and that the problem would be outside their parts of system.

because it's not an electrical fault.

the best solution has been offered many times. make or buy an antenna isolator.

Bye. Jasen

Amazingly, as I mentioned on here several times, I did so, to no avail.

I believe that you later said what you got at radio shack was a noise filter. Did you get an isolator afterwards? Did you report test results for that? Please note that a correct isolator would have broken the ground loop.