Ticking noise in Audio Research Reference CD7


Hi,
I have a relatively new CD7 (probably with about 1,500 hours on it) and it recently started making this ticking noise each time I press "play" or move between tracks ("forward" or "backward"). While just playing the noise isn't there.

Any ideas where this noise could be coming from/caused by?

Thanks.
amuseb
Post removed 
Hi Elizabeth, I've opened the unit but can't see the rails. Do I have to also lift the CD tray to access those?
Is there anywhere where this process is described with pics for my layman self?
Also, I live in a very big city and there's a lot of dust/dirt/smog in the air at all times. How do you clean the guts of those units (CD 7, Ref 5, etc) that have practically no protection from all that dirt?
Thanks.
Did you expose the mechanism completely ? You need to take the player's top lid off first, then the square black metal element that covers the mechanism (it is beeing hold by 4 screws), and then the black plastic part that covers the rails (it is beeing hold by 4 allen bolts AFAIR).