But remember this is not a TV repair forum. It sounds like a board or tab bond failure but only a tech that sees the set would diagnose this.
Check your warranty and if in the USA, register your set for 3 more months if it's on the edge.
RE: Samsung PN58C550
I'm having bleed-over lines, mostly black and mostly on commercials when block lettering in black appears. The image goes across the whole screen and is about 4 inches top to bottom. It does happen on regular programming but not very often. I did not find any firmware update newer than what is already on the set. Mostly this TV has a great picture but this issue is very annoying and does not happen on my Panasonic or Philips Plasma TV's. Does anyone know of a fix or cause for this?