LN36.201 is not a transformer It's a ballast. It's an inductive current limiter - a series coil for your tube. Without it your tube would drain, once ignited, as much current as there is available until the fuse blows.
Because they are coils, they also act as electric magnets and vibrate. That makes the sound if anything is slightly loose. A few drops of glue can fix the problem, if the moving (=buzzing) seam is visible and has no electricity. You can easily test if something is loose by pressing the ballasts by hand and this way suppressing the vibration.
250V is a substantial overvoltage. It makes the ballasts more noisy because the current is higher. The current in theory is at 250V only 8,6 % bigger than at 230V. In practice the difference is bigger because the iron core in the ballast start to get saturated and it does not limit the current as effectively.
Addendum: Light dimmers and DC-->AC Mains converters often produce distorted, non-sinusoidal output voltages. Those can easily to be heard from the ballasts as increased buzzing. Ballasts are originally designed for sinusoidal AC voltage.