Flickering horizontal lines across monitor occurs periodically throughout the day.

I have a new HP Pavilion 32 inch monitor.  Periodically throughout the day I have flickering horizontal lines across the screen.  This is very irritating and makes the monitor unusable.  For reasons to complicated to explain, I am sure it is NOT a problem with the monitor or my computer.  I am sure it is a network signal problem.  What is the solution to my problem?  I have tried resetting the modem several times but that doesn't help.