I had those problems a good bit when I first got my Wii. It occasionally does it here and there. Most of the time it does that horrid clicking sound, like some tiny plastic hammers are beating my disc to death. But it must be something else since none of my games are even nicked. I've had the occasional disc read error, but that's pretty rare. As far as games locking up, I've had a single instance of this happening with Zelda and Fire Emblem(when resetting), but multiple times with rush-jobs like Madden 08 and Red Steel(but that's not what you're talking about).
If it's happening that often, it must be a hardware problem. Get it replaced while it's under warranty. I wish I had done mine when I had the chance, but I'm just paranoid about that kind of thing. My Wii works fine 99% of the time, though I still get the occasional scare.
If it's working horizontal, and not vertical, it could be a problem like people were having with the PS2. I believe with the PS2 it often had to do with a cheap plastic wheel that was used to spin the discs. From what I read it would warp over time with use and gravity, which is why some people's worked better after switching it to horizontal from vertical.
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