I don't understand why different discs are louder and some are silent, but occasionally (usually) I hear quite a bit of mechanical noise from the spinning disc / components. Not a constant grind, but a 'chirping'. Maybe the laser isn't tracking well? Picture and sound are fine, but the mechanical racket can be horrible. Any ideas what the problem may be and any solution? RCA LDR-310 (1992) I keep a backup player at a buddy's house. Maybe a swap is in order, but it's the infamous MDP-333 with a bad door, and it's not as pretty. Thanks for any advice.