In FCP7 the easiest way round this was to add a simple audio cross fade. You can't do this in FCPX. Why not? Why the fuck not? Because it's fucking stupid that's why.
But don't worry because Alex Gollner isn't stupid and he has created an audio only cross fade for FCPX. Not only that, it's free.
Download the audio only transition from Alex4D.
Thanks Alex. You help heal the pain and hurt of FCPX.