New computers with magnets shouldn't make a ticking noise unless the reader is too close to the magnet as it passes. Just push the reader away a fraction of an inch, and the ticking noise will disappear.
+1 ... I have never heard any noise from any bicycle computer and have been riding with our local club for nearly 16yrs. If you hear noise ... the magnet and receiver are touching as the magnet goes by. It just needs to be adjusted.