Problems watching movies on iTunes -- lagging video, distorted audio

Question

Hello. I have a black MacBook running Mac OS X 10.5.8 (Leopard) and iTunes 9.0.2, and I'm having some problems. It's been going on for a few weeks now, and is worse some days than others, but the overall trend has been downward, so I wanted to try to get some help before it gets any worse.
The problem occurs when I try to watch movies on iTunes. I haven't had any problems with any other aspect of iTunes, although I don't really use any other aspects of iTunes at the moment besides the iTunes Store (I don't listen to music through iTunes or anything). Anyways, here's the problem:
Sometimes, when I'm watching a movie on iTunes, it will randomly (or seemingly randomly) glitch on me. I use the general term "glitch" here because the problem can manifest itself in one of a few different ways:
1.) The picture will freeze for a quick moment (less than a second usually) and skip forward real quick to catch up, and then sometimes, after it does this, it will go back to normal and keep playing the movie correctly. Other times after it does this, however, it will continue playing the movie, but with lagging video. When I say "lagging video", I mean that the video is slowed down, as if in slow motion. The audio remains normal. This only seems to happen in full screen mode (although I don't really watch movies any other way), so when it happens, I can generally hit escape to go back to regular viewing mode and it will fix itself, although sometimes I have to quit out of iTunes and reopen it.
2.) On rare occasions, instead of the video lagging problem, the picture will freeze all together, and if I recall correctly, the application always freezes with it.
3.) Less commonly than the video problem, the audio will become distorted. This usually occurs separately from the video issue, but can occur simultaneously as well. When this happens, the audio gets really scratchy and distorted, as if it was being filtered through a low quality children's boom box microphone. iek the video problem, this problem occurs randomly in the middle of watching the movie, but unlike the video problem, this problem persists after I quit out of iTunes. Quitting iTunes does not fix the problem in this case, unlike with the video lagging. When I quit iTunes, the distorted audio remains an issue an any application I use, and I have to wait awhile for it to go away on its own. So, unlike the video lagging, this audio issue seems to exist outside of iTunes, although it always starts with iTunes.
Can anyone help me figure out what is going on here? I've looked for patterns in other applications that are open during the times these problems occur, but haven't found any. I do have Norton AntiVirus installed on my computer, and I did notice awhile ago that any time I try to watch a movie on iTunes while I have a virus scan going on, I always get a glitch on iTunes, so I stopped running those two applications at the same time a long time ago, but I still have the problem. Should I try reinstalling iTunes? If I do this, will I lose any of the music or movies or apps that are in iTunes? I would assume not, but I just want to make sure I don't need to back anything up if I want to reinstall iTunes.
Thanks in advance for any help anyone can offer.

Answer 1

Not sure why this question is labeled as "answered" since there are no answers in the thread?
I'm having the same issue with the extremely distorted audio track on itunes video. It's worst on the speech, which is hard to hear, garbled, a lot of scratchy noise overtop of it; the music tracks are somewhat better (and much much louder). This started a bit ago and was intermittent at first, now very bad, can;t get rid of it.
I have a lot of itunes video, and since it is all protected, to my knowledge it is not playable through any other player... so this is a real problem. Reinstalling itunes (9.2.1) did not help. Sometimes VLC also distorts sound (on other video), more often that's fine but itunes is not.
I would love to have a solution to this-- my video library is not much use.