When LW is busy or has been on for a long time, the player suffers. I'd recommend disabling the LW media player. Go to your LW pref options (keyboard shortcut: Command & Comma keys ⌘ ,) & select player & disable it. Then iTunes will act as your player instead. Alternatively use Audion (click on link) or VLC as your default players. (Audion cannot play m4a files however, but can play mp3pro & ogg vorbis files both of which iTunes cannot play.)