Most do but it depends on where you live and how new your cyclometer is. Newer designs are much better at ignoring rf interference than the first models.

My funniest (funny=strange, not funny=hahaha) experience with RF interference was the heart rate monitor a friend was using at his doctor's recommendation after heart surgery a few years ago. It was a cheap, non-coded Nashbar unit since he didn't want to put out lot of money for temporary use.

We were riding easily and his heart rate was in the desired range when we passed an electrical substation. All of the sudden his heart rate reading spikes to 250 and then falls to zero! Talk about panic. It took a moment for us to realize why the reading suddenly got so alarming and it returned to normal about 1/4 mile later. His next purchase was an expensive but coded Polar monitor.