I just bought a DC28 refurb and while it works amazing, it's definitely making a high-pitched "squeal" type of noise when you push the machine forward. It's bad when you first start vacuuming...almost like a slightly quieter version of wood being cut on a table saw. It goes a away a little bit after a few minutes, and doesn't seem to happen when you pull the machine backwards, but it's definitely there, and definitely annoying.

Anyone have any ideas?

No idea I'm afraid (sounds like something inside coming into contact with the motor housing or worse still the fan itself). If you can I would return it.

The same on my DC24...