Issues with audio on certain clips

Hi every one, I'm having issues with some of my clips in adobe premiere pro. I think the issue may have arisen due to the formats of my video - some was shot in 720/25p whereas others were shot in 108025p. In this case I opened a project for the 1080 footage, exported it, and imported it into the project with 720 footage. The audio for the 1080 files is now terrible (very fuzzy) and originally there were two thin black vertical lines down both the left and right side of the 1080 clips that had been converted to 720. At some point, (I'm not sure when) little squiggly white lines have appeared in the black lines, which move according to the audio of the clip. I tried to attach a screen shot, but the website does not accept bitmaps and when saved as a jpeg the lines disappear... I'm very new to editing and premiere pro so I have no idea what I've done or how to fix it. Your help would be much appreciated!

Cheers, Gill