For the last couple of days I have had a creaking sound coming from my Coker when I pedaled it hard. This was, of course, infrequent for me. Usually the Coker is very stealthy, much more so than a bicycle, because there is no chain or derailleur noise. I thought at first that it might be spoke tension but I tested that and it was OK. The pedals are new and I didn’t check them. The bearings turn freely and noiselessly. I ride curbs on my daily commute and hop off frequently (I, of course, mean to do that) but didn’t think that I stressed the cranks enough to loosen them. My cranks have been on for a couple thousand miles and, after the first few days of pedaling and retightening, they have given me no audible problems. I broke down and checked them last night. Sure enough, there was some play when I really pushed hard on the cranks by hand. I retightened them with a 14mm socket and both sides advanced more than a half turn. Today the Coker was its old stealthy self again. I spent my commute today sneaking up on pedestrians and more advanced wildlife and scaring the bejeesus out of them. I’d forgotten how fun that was.
Moral: It could be anything but it’s always the last thing you check.