Whirlpool Duet electric dryer- three fast beeps when you press the start cycle button
This problem is caused a bad door switch. Here's the link to the door switch, click the picture:
You can test using an ohmmeter. There are 3 prongs on switch, identified as C,NC, and NO.
C-NC should be closed circuit until you push switch and then it should be open.
C-NO should be open circuit until you push switch and then read closed.
Buying the switch through this site is a risk-free proposition because you can return the switch for a refund if that doesn't fix it.