Post a SysCheck.
Also, just because your Wii can read Wii discs doesn't mean the drive isn't damaged in some way. My Wii had an issue where it sounded like a lawn mower while reading discs. Wii games worked, GCN game didn't. I got the drive replaced and it fixed the problem.
I'm not saying this is the case for you though, just saying don't rule it out. We'll check your mod to rule that out.