When the block heater is plugged in, is it supposed to vibrate? I have a new 2011 Sierra Duramax. Any input would be appreciated, thank you.

Not sure about the vibration but there is a noticable sound on all the others I've owned.
Where do you feel this vibration? On the block

Well of course it isnt doing it now. It might have been because it was the first time that I used it and that the engine was already warm from driving. But have had it plugged in for a couple hours now and it seems to be doing it job. Thanks for the information though, appreciate your reply.

You may want to check your owners manual needs to be below a certain temp before you need to plug in.