Hissing Sound In TV
At the starting my TV produced heave hissing and wiring noise. After few minutes it will disappear. But picture and sound are clear.
Hissing sound usually are caused by transformer, inductor/coil due to loose lamination of the core. An overheated transformer also could cause hissing sound. This is why you need to know if the transformer runs hot or not. If it is very hot and too hot to be touched then suspect a bad transformer otherwise suspect a loose lamination of the core. Some repair techs called hissing sound as noise or even high pitch sound.
If you came across an equipment that work normally except for the hissing sound, the first thing you do is to gently hit the transformer or even the coil with the handle of the screw driver. If there is no changes probably either the transformer itself is bad or the corresponding component have problem. If the transformer is quite down after you hit it this means there is loose lamination of the core.
What you can do in this case is to dip the transformer into shellac for about an hour and then let it dry for a day. The hissing sound will usually go off. I had done that few times and each time it worked.