In my experience, the seat and/or seatpost seem to be the root cause of noises that sound like they're coming from somewhere else.
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RIP 01/08/25...2022 Trek Supercaliber, 2018 Storck Fascenario.3 Platinum, 2018 Trek Procaliber SL Singlespeed, 2017 Bear BR1, 2003 Time VX Special Pro, 2001 Colnago VIP, 1999 Trek 9900 singlespeed, 1977 Nishiki ONP