Ipod skips during playback after I updated the software?

Today, I synced my ipod for the first time in about 12 months. This morning I listened to the ipod in my car and all was working well. When I plugged in the ipod to the computer, it asked to update the Ipod software, so I did. Then I added about 10 new songs to the ipod and synced it. But now when I play those songs, it makes a loud buzzing sound for about 1/2 second. And the buzzing sound repeats randomly about every 5-10 seconds. It does it on the new songs and the old ones that worked only hours ago, before the update. I tried burning those same songs onto a CD, and that plays fine, so the song files are not corrupted. Any idea where the buzzing noise is coming from? How can I undo the Ipod software update?