Hi
If there is a poor connection some arcing may take place with a smell like ozone; one poor connection could be if brushes on the motor are worn, they are a service item.
Years ago I had a similar problem on a Hoover, bought cheaply as it made loud cracking noises in a random way. The fault was declared on this newish machine, I thought I could fix it. I could, a capacitor connection was arcing to nearby metal, I moved it away, no more cracking noises, used it for years.
A Barton
December 2007