I wanted to reply to this thread to let you all know that when this problem occurs, the printer does not zero out toner cartridges when it displays the empty warning! I just had it happen again with Magenta, a color my printer seems to really hate! I went through four different carts, one empty, two high capacity full/half-full (respectively), and one standard capacity (full) and it said empty on all of them.
Finally, out of desperation, I pulled out the standard cart that was in the Magenta slot, the last cart I put in. I took one of the full high capacity toners that already showed as empty at least twice if not three times at this point. Powered off the printer using the rear power button. While it was powered off, I spun the little white plastic wheel on the side of the toner in the correct/spinnable direction about three rotations. Shook the toner, put it back in and powered up the printer using the rear power button. After a little noisy hemming and hewing, the noise stopped, the printer booted up and showed 100% in the high capacity Magenta slot.
The moral of the story is that it does not zero out the carts (not sure about the first one when the problem starts, but certainly not any subsequent carts that are inserted). It is just a measure of twiddling with the carts and spinning the wheel on the side to finally get it to work. Of course if you have a toner jam, you'll have to clear it out before you can hope to get it to work. BTW, this happened to me on a pretty humid day, if it is of any consequence, so it may be worthwhile to try again on a dry day if you can't fix the problem.
I believe you need at least two carts and to alternate between them, or it will forever show empty, but this is only speculation. The important part is that it does not appear to zero out the carts, as some people suspected, which would be disastrous for new carts.
I think the fix for this is to spin that wheel in its intended direction a good five revolutions, at least, and things start to work again (unless yours is clogged of course, then nothing you do with the carts will fix it).
I believe that the grinding sound that you hear is due to either wear on whatever spins the carts or an underpowered motor. Spinning the cart manually probably reduces the friction in the mechanism of the cart enough for the printer to finally be able to latch on and spin it further, clearing the empty error state (finally!).
This problem is probably exacerbated by humidity within the carts, because the toner may become more congealed and make that wheel more difficult to spin. Shaking the toner also helps to make it more uniform within the cart and may help loosen it up.
