I'm also experiencing some odd noises.I heard it first when doing 75 mph on a perfect new piece of road. Instantly thought it was the wheel bearings.
Yet when driving more i sometims could hear it when doing only 30 mph on some roads and also, the noise doesnt get worse when i increase speed.
I popped into my honda garage and they were incredibly willing to help me diagnose the problem.
They took the car on a test drive and agreed with me there was a slight humming - buzzing noise.
When the car was on the ramp, they checked the front wheels as that is were the sound is coming from but there was zero noise when we spun the wheels (apart from the pads ever so slightly touching the disc) and there was also no play whatsoever in the bearing.
So i think (hope) that my tyres are getting so low that they are making this noise.
I'm running uniroyal rainsports 2 all round and they have almost covered 40 000 km, thread depth is still legal but i was planning on buying new tyres after the winter.
If the noise doesnt get worse over time, i guess its a tyre problem.
Anyway, this is going to cost me
EDIT: Perhaps its also worth mentioning that its virtually impossible to hear the noise with the a/c and the radio on normal