Canon XL2 Lens

Hi gang,
I'm hoping someone can help me or shed some light for me. I purchased the XL2 about a year ago, to replace my XL1S. It's been a good camera so far, but recently I've noticed something that really concerns me. My (small) production company has been hired to shoot a local teen full contact football league. I've noticed that at times, it seems as if the lens "shifts" just a tiny bit when focusing on the players. At first I thought it was just my imagination, but no. Sometimes the image will shift, or, like a frame or two "clunk" either horizontally or vertically. It seems to be happening a little more often as well now. I've sent Canon an email asking if this was a known issue, and their standard form email reply was to send it in to be repaired. I'd like to see if anyone has any info before I commit to sending my camera out and spend a lot of money in shipping and time. Thanks! Al