William Driscoll

6000 HD from Costco. Mine does it too. I think this may just be a normal
noise. You can create the noise with no attachment using your hand.

Edit!! After more reading I have determined this sound is NOT NORMAL. I
swapped my unit out for another one and the sound went away completely. 

Federico Carbonetti

hi! Did you understand what was the reason for this click? Mine (1 week
old) does it too and I don’t know if I have to ship it back… Thanks for
your answer! bye

Eric Ste-Marie

I have the exact same problem, doing the same thing with the same
attachment. Did you ever find out the cause?

Nicole Heroux

I just bought the Kitchenaid Professionnal 6000 HD from Costco and at the
firt try, I have exactly the same problem… You got some answer?