Hello blissteach,
I just wanted to make sure that it was still in tact, yes once you push down on the tab and close the ADF you can hear it click back up, that is ok and normal functionality of the printer. I would like to make sure the 8600 firmware is up to date.
On the front panel of your printer please select the ePrint (web services) button, see image below:
Once you are in the ePrint menu, I would like you to scroll down to the update option and check for updates, if you have this set to update automatically it may already be up to date. I would like you to post back here with the results if unsuccessful and I will send you a private message on the Forum so we can continue from there.
I appreciate all your efforts.
Thanks again,