Canon Pixma e400. message says there is a paper jam, but I can't see any jammed paper inside.

[akoppa]

I have the same problem or similar.  Sometimes, when the printer starts printing I hear some unusual sounds. Then the paper jams. I pull the jammed paper and try again. The printer hangs and the popup error shows up.
I fixed it switching off the printer to check the printer head position. After switching off the head should remain all the way to the left, however, after a paper jam the head stops in the middle, so I push it all the way to the left or right. Then I try again and this time the printer prints normally.

[ccorleyjd]

I have the TR4520 and I'm having this same problem.  I am going to try your solution. I wondered if the problem might be a design flaw, i.e., the printer cartridges are too close to where the printed page exists the machine?