That would be one very impressive DSP hack if you could eliminate the motor and other contact sounds. I highly doubt that you could cancel it out effectively but it is so tempting to try this to see how far you'd get.

A couple of approaches would be:

- bandpass filter in human voice range

- two mikes, only one facing outward, opposite polarity

- a lot of mechanical isolation

- a digital sample of the audio stored and subtracted from the input

And more such tricks. It would be a very interesting project to see how far you could push that.

Part of me thinks this story is made up just to scare people. Why would it be public info if they were actually trying to catch people like this?

You're assuming they didn't just put a little rechargeable battery in the vacuum too. Id assume people weren't doing drug deals while people were shop-vacuuming. Id definitely want to be able to film while it was off.

Lots of vibration too, seems like video would be difficult.