Extractor fan air noise

I have just relocated our 4 inch inline extractor fan in the loft to make the run from the inlet in the bathroom to the outlet in the soffit as short and as straight as possible.

The run is now no more than a couple of meters and i have done it in solid pipe rather than the corrugated bendy 'snake'. In the loft the fan is whisper quiet, but now having 'upgraded' to solid pipework and moved the fan slightly closer to the inlet, the air noise in the bathroom is quite intrusive.

Is there any way to quieten down the air noise in the bathroom? Any suggestions greatly appreciated!

Change back to flexi , rigid plastic transmits the noise more effectively.

Could a short piece of flexi between the fan and the inlet help or does it need a longer length to disturb the airflow more?

By changing to smooth rigid pipe i had assumed the airflow would be smoother and therefore quieter!

I guess it’s vibrations in the pipe wall itself, not in the air inside the pipe.