Ive had a bit of a search this morning and there are no reports anywhere of any turbo cars making a humming noise.....although we all describe things differently.
Whistling is the common term for turbo noise, as its the sound of the compressor inside the turbo spinning up to speed.
Im wondering if it's just the engine noise you are hearing rather than just the turbo? Also does it happen at very low revs? The turbo will not be doing hardly anything close to idle, perhaps try accelerating from idle to say 1300-1500 revs, if the noise is the same then I'd guess it's just the engine noise rather than a turbo issue.
This doesn't make it right by any means but some have said the engine is not as quiet as expected.