Denon DVD-2910 excessive vibration?

I was wondering if it is normal for the Denon 2910 to vibrate with authority? While playing CDs the vibration starts out strong on track 1 and then slowly diminishes with each track to nothing by the time the CD is over. I can't imagine the vibration is good for sound qualty.
What bloomphoto said really makes sense to me - I have noticed the same exact thing, and the "imbalanced disc" idea crossed my mind, but for some reason I dismissed that. Like I said before, my 2910 seems to do it with sacd's, but I bet that certain other discs would too. I havn't heard or seen effects from it, but how would I know if there is a problem - maybe I'm just used to hearing the problem.
I have not had any problems with my SACDs, but if the disk is off balance, it shouldn't matter what type of disk it is.
I received a demo DVD from B&W. It made my whole cabinet shake the player was vibrating so much. I read in an online forum that other people had that problem with that demo disk. I contacted B&W and they sent me another. No vibration.
What Wahoo_Envy describes as the CD vibrating on the first few tracks and then vibrating less as the disk is playing I believe is due to the fact that the laser tracks from the inside out. As the laser moves toward the outside edge of the disk, the disk spins slower. Thus less vibration.
I also tried updating my firmware and re-initialized my player. That did not make any significant difference as far as vibration with the problematic disks.
My Denon 2200 has an extremely bad vibration with most SACD and DVD-A discs. There is no vibration with DVD or CD. The vibration gets less and less as the tracks go up, just like yours. It also runs very warm, almost hot to the touch.
After searching posts, it sounds like this a common problem with a few Denon models. The unit sounds good; although, I have mostly listened to DVD-A and SACDs now that I have the capability and have purchased at least a dozen high res titles.

A couple of years ago, two of my friends have bought new DVD-2900s after consulting with me and now one player doesn't read but every other disc. The other player quit reading discs all together. I almost feel guilty.

In the past, I have been a very loyal Denon consumer, but now I am starting to have my doubts.

I will call Denon again and tell them that re-intializing did not resolve the problem. This unit may be on its way back to the dealer. I am not sure there are any other manufacturers who offer reliable units at a similiar price point with the same build quality, performance and features.
Here is a very good article which discusses CD balance issues Redbook CDs have a particular problem with high speed drives due to the lower tolerance standards for the center hole.
The Denon 2910 spins at a high speed and has a large buffer. I do believe that is why it is less tolerant of unbalanced disks.