Problem with cable signal pixelation

Recently A cable company ask us to do some power monitoring at a few of there subscribers houses. Apparently, their having trouble with the television picture tiling, or pixelating in these houses. They have tried everything they can think of. The company thought that it might be a power quality problem. I thought maybe ferrite cores on the coaxial cable might help. We are setting up a Hioki 3196 on the power lines coming into one of the houses to give us some insight into the problem. Does anyone have any possible solutions?
I installed a hioki 3196 on sight per-request of the cable company. I sure would like to have the answer for them, even if it’s not the power. Does anyone have any possible answer? The coax is shielded. I did notice the PVC conduit, that the main feed is pulled into the building in, is full of water. Could this effect the signal? Pixelation is only occurring on certain channels. The problem is occurring in an apartment complex. More than one unit is being affected and all the apartments are feed from one transformer. I know nothing about cable installations. Any ideas would be appreciated