Look for blockages in the air inlet holes on the shroud and the ball.
Dyson fan noise problem.
Dyson fans are notorious for getting clogged with dust at the bottom section and the turbine blades.
Get expert help troubleshooting from dyson to get the most out of your machine.
The airflow should be strong enough to lift a sheet of newspaper past 45 degrees.
Try to clean the blower section of the fan.
Unplug your dyson personal purifying fan from the mains electricity supply before cleaning your machine.
The fan has a strong smooth airflow when switched on.
This may be causing the motor to work extra hard resulting in the noise i have posted an article on how to do this at the following link.