Audio distorted on some things, fine on others.

[Hekabe]

Alright, here's my problem. My audio is distorted on some videos/songs, but not others. It first happened on my Windows XP install. I started a Youtube video and the sound sounded horrible, like my cord was shorting out. I immediately though it was a hardware problem, since my sound card is dying a slow, painful death and my headphones are brand new. But when I wiggled around the connection (which usually fixes the problem) with no results, I decided to troubleshoot and try another Youtube video and the sound was completely normal (I use Chrome on Windows and Chromium on Lubuntu). I switched to my Lubuntu install, and not only did those videos display the same charcteristics, a downloaded movie began doing it as well, in Gnome Mplayer. I'm completely lost. Any help?
I'm running Lubuntu 12.04 on a Dell Dimension D630.

[HiImTye]

is it only specific videos? could be a hardware decoding issue. check if its specific codecs, or codec settings that cause it

[Hekabe]

It doesn't seem to be limited to any specific videos. There's a whole folder of videos which have the exact same issue, which persists on multiple different video players.

[HiImTye]

alright, let's skip past the codecs for a bit. is there any audio that plays fine?

[Hekabe]

Yeah. Some videos, both streaming and offline, are completely normal. On closer examination, by the way, on the ones that are messed up it sounds like they have a really horrible EQ (a.k.a music sounds normal, except you can't hear the vocals, or vice versa), but it can't be any kind of master sound card EQ, because some stuff sounds fine, and it can't be software EQ, because I did a clean install of VLC to play the stuff and it sounds the same.

[HiImTye]

what do the audio the plays fine have in common, and what differs in the audio that doesn't?

[Hekabe]

Currently, as far as I can tell, all my local files have distorted audio. MP4s, AVIs, MP3s and WAVs are what those would be. On Youtube, what I've tried is some trailers for GTA5 (distorted), some random music videos (all distorted) and some soundtrack music from multiple channels (all fine). For comparison, I tried streaming from another site, and the audio was fine.