I agree with Murdochchat in-line fans are normally quiet.If you put your hand on the fan or the ducting while it's running can you feel excessive vibration, that could indicate a faulty fan. Is the air intake loose in the ceiling cladding. I would not think flexible ducting would make any difference. Moving the fan further away from the intake might improve it.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local