Carpets are great noise mufflers for vacuums. Most of the noise comes from the bottom of the vacuum, and when you don't have carpet under there, it is at least three times as loud.
I have a noise problem in mine, but I think the reason is related to a vibration problem too. The handle gets really uncomfortable because it feels like something is ready to rust apart. I can hear it squeak when I shut it down
Sterling, April 2008