Re: Engine noise at warm up
Your bike is about to blow. I would run away as fast as possible. The pistons are hitting the valves, the cam chain is slapping the side of the block, the valves are loose, the injectors are clogged, the crank is wobbling, the bearings are locking up, the clutch basket has come unglued, and you may be low on blinker fluid. You might need to change your exhaust bearings as well.
All joking aside; The CBR is known for making noises, even after warm-up. When you make the power these bikes make something has to tick and click. You're going to hear all sorts of things you don't hear from your car because you are much closer to the non-insulated engine.
At warm-up you are likely hearing the clutch-basket rattle. The bike sits on the left side and there is no oil on the plates. It takes a moment for everything to get lubed, even after you have oil pressure. This is why it's important not to rev the bike to a high RPM before the bike is fully warm.
Take a moment to pull in the clutch lever and the noise will settle some. You could also sit on the bike and lean to the right and the noise will calm as well.
There is a lot going on in that motor, you are going to hear some noises, trust me, you're safe.