Creak source suggestions

I have a creak from my carbon frameset Cervelo R3SL with full 1osp Duraace groupset and external hollowtec II BB. I have isolated it to drivetrain as creaks when out of saddle or none handed. I’ve stripped crankset down and reassembled. Creak is not in any particular time wrt to crank, wheel or chain rotation. It is quiet to start and creaks after say 10 miles, quietening again later. Perhaps this is some friction that warms grease or such like. The crankset is 10 years old and on its 2nd big ring. I have noticed that the axle has suffered some minor corrosion on the bearing surfaces. I’ve cleaned this up with 1000 grit. But I am wondering if the issue is connected. Wheels are pretty new, so I’d be surprised if that was the issue. Otherwise it is flawless. Any ideas?