Whirlpool washer spins up really fast, then slows to a stop.

We bought our washer back in late 2011. Since then it has been working great, but recently it's been acting up. It runs through it's paces, fills with water, agitates nicely, but when it hits the 4 minutes left mark, it will spin up to a pretty fast speed, then begin to spin down to a stop. The timer then resets back to 17 minutes and does it all over again.

Any help on this issue will be of great appreciation!
Thanks!