I recently started using a MagicShine and, yes, it is great. However, the light does interfere with the operation of my wireless cyclometer. Is there a way to shield the light? Does placement of the light and/or the power pack on the bars or bike make a difference?
Moving the battery further away also works, or at least it did for my Dinotte and Sigma 1606L. I put thebattery pack under the top tube just behind the head tube, which let me put the light itself on the bars right next to stem. The computer was in the same position on the bars, on the other side of the stem. Both were out of the way, and didn't limit hand position at all.
You want to avoid placing the battery pack too close to the head unit, and also not directly in line between the head unit and fork-mounted sensor.
Some bike computers are more heavily influenced than others. I mount my batteries on the stem RIGHT NEXT to the computer. One is a Sigma Rox9.0, the other isa Specialized (whatever they're selling right now wireless). I've only experienced interference once out of the Specialized. NEVER from the Rox. Of course, I'm using a TridenX, not the magicshine. Their may be some design there that minimizes wireless interference that the Magicshine does not possess.
Get a ferrite bead and install it right near the lighthead, running the cable through it a few times. (Don't get it from this site, however -- I used their link because they had a good picture of it and a shot of it in use. Our local Frys has them, and Radio Shack might, as would any local ham radio shop.)
The most likely cause of the noise is that the light is being flashed on and off very fast (that's how they regulate the brightness in an efficient way) and this is generating noise, and the noise is being radiated by the power lead -- it's acting as an antenna. The ferrite bead will help attenuate that. Other options include moving the lighthead, wire and/or battery further away from the cyclocomputer receiver.