I have this prob as well with mine, i found a really easy solution...theres some buttons to the right of the steering wheel underneath the windscreen wipers stalk, if you hold in the top button on the back of this, the noise starts to disappear....I do believe this is called the volume button?? lol :rasp:
Only joking mate... I do actually have this prob too, someone said there is a little fan inside the interior light housing and this can either be taken out and lubricated or you can get a new one from renault for less than a tenner!
Do a search on the forums for 'humming' and you will see a few thread like this with answers...
Hope that helps!