helllllp funny lines

hiya guys new to this forum and only got a ps3 sunday and having a problem lol, basically when i play ninja gaden sigma i get horozontal lines appear and move up and down on the picture( see through lines like wobbly picture in certain place), it only seems to happen when either im fighting a few people or theres a bit going on, on the level it only happens on this game though all others are fine can someone help please as its really annoying,
p.s im playing through hdmi 1080i