Do you often switch it up, like a cool little rhythmic pattern pops up in your head and you think "oh, that needs a melody"?
the vast majority of songwriting for me is based on the melody/lyric, but a small number of times i have found a certain groove or chord sequence that i think is basis for a song, so it is entered into the song list. i don't recall if any of those have ever made it to the next step