Post hoc ergo propter hoc
Since moving to Ann Arbor, I’ve noticed that occasionally there’s a strange Morse codelike static on radios or speakers. It made me wonder about the electrical system on the campus where I work and the town where I live. What it did not make me wonder about is the cellphone that I carry. When I moved here, I switched from Sprint, a CDM carrier, to Cingular, which is a GSM carrier. I learned from Joho the Blog: Rhythmic static that this is a feature of GSM cellphones, something I verified by turning my phone off when it next happened.
Interesting example of the difficulty of inferring causes from correlations.