I'd suggest a combination of both mcav and cpr's suggestions. Highlight the notes themselves instead of the area around them. Drop the jumpy marker and replace it with a smoothly moving, constant speed vertical marker. It's a commonly recognized and understood element (used in pretty much any and every audio production / recording software). It also gives the viewer a better sense of the tempo. Remember, tempo can change drastically over the course of a song; the current marker doesn't demonstrate the difference between playing shorter notes at a slower tempo and longer notes at a faster tempo.