Cateye magnet not working with Sigma computer

You shouldn't hear a "tick" as the magnet goes around - this suggests you might not have it lined up correctly (or it has moved) and it is hitting on something. Also, check the distance between the magnet and sensor - they need to be fairly close together at the point when they pass each other. (if it worked for a while and then stopped, it suggests something has moved and the alignment is no longer correct)

[/QUOTE]You shouldn't hear a "tick" as the magnet goes around - this suggests you might not have it lined up correctly (or it has moved) and it is hitting on something.

Mine makes a noise on every revolution and this will be normal. I think there is another magnet in the pickup that moves and by doing so creates an electrical current, hence a readout. The noise you can hear (just) is the magnet in the pickup moving.
I also have a Sigma and for the blade spokes exchanged the magnet with a cheapy off the MTB and it works perfectly. Something to watch is that you don't have the magnet too close to the rim...the further out it is the faster it moves, to the stage that the pickup cannot register the magnet going past.
Halcyon1