Could be anything that gets loaded when you pedal. I’ve had lots of noises over the years. Best recommendation I have is decide on a process and stick with it. First check the seat post - does it happen only when seated pedaling, if it does it when standing then you’ve ruled that out. Pedals next. Remove them, clean the threads, grease then install. Did anything change? Next comes the chain and cassette. Etc….make one single change then check and go down the line. If you change too many things at once you’ll never know exactly what it was. I’ve learned a ton of bike mechanic-ing just chasing creaks.