Importing clips into the timeline only imports video, not audio - weird issue just started occuring

I've never had this issue before, but just recently, when I drag an imported video clip onto the timeline, it only puts the video portion of the video onto it. The audio portion is left blank.

The only way to prevent this is to drag the video into a new sequence, which imports it correctly. So I've been able to use the annoying workaround of importing each clip into its own sequence, then copying and pasting it into the master sequence, then deleting the new sequence.

Did I accidentally check some box that caused this to happen? How do I fix this?