I changed my strings and when I went to play, BZZZZT! A terrible buzz. After much more detective work than I should have done, including removing the resonator and using a sponge to dampen various parts of the banjo I found it.
The D string (4th string) was slightly raised against the tailpiece. Giving it a firm press got rid of the buzz.
Nothing earth shattering here. Just a little advice that might help someone else in the same situation.