As mentioned the noise is airflow related not mechanical. If the noise wasn't there, us 146 pilots wouldn't know thet the flaps were travelling!
In the co I work for mention of the noise is indeed made towards the end of each safety demo, to the affect that,
"shortly after take off and prior to landing you will hear an airflow induced noise associated with the extension and retraction of the wing flaps. This noise is normal." 
I'd be really interested to know if the 146 was to be newly certified in 2004, would certification be granted, given said noise, and not withstanding some of the other design characteristics of the 146.