Can you share the specs. of those Imported Clips, and especially the Audio CODEC inside?
Now, there is a common reason for Audio to either not show up, or perhaps be truncated - failure to complete Conforming. This ARTICLE goes into more detail. As PrPro edits/plays back from the Conformed Audio files (CFA's), the Conforming process is very important.
Good luck, and please let us know a bit more,