I guess it wasn't just my computer after all. Someone else spotted the graphics glitch in the C64 game. So I'll wait.
I decided to resume work on my Game Boy game. For a lark, I went into the usually empty Game Boy programming forum. To my surprise, there was an answer from someone. Feedback! Someone mentioned a few things to work on, one of them being to lower the pitch of the music. So I did. But because I did, I found the bass notes to be too low, so I cut them out. That, and I got frustrated because I couldn't get them to be in the same pitch yet be lowered.
But I got the treble working okay. I had to change the note values since I lowered the NR12_REG from 0x87 to 0x86, meaning a whole new set of notes to try to figure out the value of. That took about a couple of hours, but I did it.