I too suffer with this problem, especially when you are cleaning a small room like a cloakroom, when the sound really intensifies. It totally hurts my ears and the kids' hamster always hides - LOL It is a high-pitched screeching sound and makes for a VERY unpleasant experience.
I have used Dyson for 16 years - I wouldn't even consider using another machine, even when living in the USA where they are not a common brand.
The DC33 however has made me re-think my view and I am no longer a happy advocate. It is so lightweight that I often pull it over when I vacuum, the noise is horrific and I am not overly impressed with its ability to pick-up successfully either. After living abroad for years, I figured that in my absence Dyson had sold out to China and was making a poor quality product whilst relying on its previous good reputation and keeping the prices up.
The "award winning customer service" member explained to me that the noise was part and parcel of their new technology and that the machine itself is light because they have removed the metal components so that more people can carry it around. I was offered an engineer (my Dyson is only 5 months old and has made this noise since its first outing!!!!) visit; but was told I would have to pay for the call-out because the problems I am experiencing sound normal for that particular design.
Needless to say I do not want to throw good money after bad and remain a very unsatisfied customer...... The noise IS REAL - find a solution Dyson!!!!!