That's normal operation. The lower speeds are made possible by some of the voltage being consumed by the resistor, which produces heat. It's common for whatever dust is on the resistor to burn off the first time it gets hot. Keep your fingers off the resistor when low speeds are selected- - - - -they will get blistered in a heartbeat.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!