Picture flickers on VCR?

Sometimes when I play a recorded tape, the picture flashes to greenish-yellow diagnal lines (from bottom left to top right) at a consistant pace -- seemingly about every second (I've never actually timed it). I've also noticed these lines as I rewind or fast-foreword almost any tape, except they come in horizontal stripes as opposed to taking up the entire screen. And the faster I fast-foreward it, the thicker the stripes become.

It is also accompanied by a somewhat subtle static sound, whenever it flickers to the diagnal lines. It doesn't happen very often, but how could I remedy it if it should happen again?