Sylvania Electronic

With or without a signal the audio buzzes and thin horizontal lines are on the screen. As time goes by (maybe ten minutes or less) the frequency of the buzzing gets less and less till I am left with normal picture and sound. If the signal is connected when the tv is first started I have a picture and sound with the buzzing and lines overshadowing them. TV works normally until it has been turned off for a few hours. Our business here is electronic repair but TV is not our forte. With a different TV hooked to the cable all is normal. The problem was occasional for months and recently became every morning when first started. Thanks!