Picture flips from color to black and white...

One day after watching the TV for a couple of hours it just flipped to black and white and then a second later flipped back to color. Each time it flips it makes a slight buzz noise. It will stay on black and white for about 2-3 seconds and then flip back to color for about 1-2 seconds and does this over and over continuously. The next day after much frustration I gave it a whack on the left side and it went back to normal, then it started all over again a few hours later and no whacks would help. My husband traded out coaxial cables with no luck and finally took the back off and found the coaxial cable jack in the tv to be a liitle loose so he traded that out and the Tv went back to normal for a day or so then slowly started repeating the same pattern.On day 3 after doing the flipping for a couple of hours I gave it another whack and it corrected the problem. On day 4 no whacking would help but after the tv had been on all day around 4pm it just all the sudden went back to normal. Today, day 5 nothing helps and the constant flipping is driving me over the edge. The set is only 6 years old but has been through a few moves. Any solution would be helpful!