When my J1s arrived, the first thing it did upon preparing to calibrate was grind horribly against the front of the case. I searched this forum and found someone describing the same problem, and someone else linked a document about how to adjust a coupling, and I tried that, and on the next startup everything went smoothly. The printer has been MOSTLY fine since then, however: sometimes when I turn it on, and sometimes when a new print begins, a big loud dull ‘thump’ will come from inside the printer. I haven’t yet identified what causes the thump, but it makes me a little nervous that it’s damaging itself somewhere, especially because I’m not even 100% certain I followed the coupling-adjusting instructions entirely correctly. Is the thump normal, or worth worrying about? (It doesn’t seem to have caused any problems yet, but I haven’t been using it for long yet, and I don’t want it to wear out sooner than it should because some part is gradually denting itself out of place.)
My Artisan does the same thing.
J1 user here: same.
Alright, if it’s happening to other folks then I guess I’ll just keep ignoring it, heh 
Same here. I think this occurs if the stepper motors are activated and jump from their random angle to the defined step angle.
If I switch in the control panel the motors off and then on again I get the same noise.
No reason to be afraid in my mind.