Creaking sounds wrong and I know the saddle rail thing, squirting lube at the clamp seems to quieten them down, but a problem I think with stupid weight weenie seat rails operating on the edge of their ability. But for major componentry to be creaking, something's stressing, moving or being allowed to move and so wear is occurring somewhere but if the metal is stressing, not good, be prepared for something failing as noise coming from structural components was always a sign something was on the way out, and am told that is why coal miners preferred wooden pit props over hydraulic as the wood would scream before it was about to fail thus giving warning to get out.
But if you consider what a squeak actually is when it emits from mechanical stuff, isn't it a high frequency scrape or judder, think of the heat being generated by the friction and what that is doing to the structure of the metal, which can be anything from removing heat treatments to creating them, either way it could be outside the design specification and stuff outside tends to fail.
But 'warming up' could be replaced with 'starting to fail' or plain 'wearing out'