Clicking noise added to audio

I have copied MTS files from an SD card to hard disk and imported these into the FCPX library as external files. When I play the clips directly from the browser (e.g. using VLC) the audio is fine. The imported files in FCPX, however,contain random clicking. This will also ultimately be in the final exported movie.

I am using FCPX 10.1.4 running on OSX 10.9.5

Does anybody else have a similar problem and, if so, is there a solution ? I have reported the issue to Apple, but nothing happens there.
The attached file contains the clicking noise. The original MTS does not have that.

Did you optimize the media? You really do need to optimize raw mts files.

Yes, I did

interestingly: if I import WITHOUT creating optimized media, the clicking will NOT occur. Therefor my conclusion is that the optimization process corrupts the audio

Additional problem is, that the clicking can be reduced by setting the background noise removal to 10% or so, but then the audio will contain a volume dip where the click was. This gives an unpleasant "pulsating" kind of sound, so that is unusable.

More info: I just did a small test using a clip with the clicking problem in iMovie: absolutely no problem. So it is definitively an FCPX issue.

A way around this (be it a very cumbersome one) is:
1. Export the audio from the original footage, e.g. using VLC, to a format accepted by FCPX, e.g. AIFF or MP4
2. Import the exported audio file into the FCPX event, containing the clip from step 1
3. In FCPX select both the imported clip and the imported audio from step 2
4. Create a synchronized clip from these
5. Right click the newly created synchronized clip and select "Open in Time line"
6. In the time line mute the audio of the original clip, leaving you with the video of the original clip and the audio
from step 1, now in sync with the video
7. Use this synchronized clip in your final video

It's a pain in the neck to work around a problem that should not be there in the first place