Sound Problems on new iMac 5K using FCPX & High Sierra 10.13.1

I just bought a new iMac 5K 27 inch computer with 16Gb of ram and am trying to complete an edit in Final Cut Pro X, however it does not play the sound from the .mts video clips.

The FCPX files are all on an external drive which loaded the project perfectly - except no sound plays on any video clip in either the timeline or the library.

I started this edit on my 2013 MacBook Pro laptop and all sound plays perfectly there.

All other sound tracks play in the timeline (music and effects) but the audio that is attached to the video camera footage is silent even though the wave forms are showing.

Does anybody have any idea why this brand new machine running High Sierra 10.13.1 will not play sound from video camera clips that my MacBook Pro will play natively on the same version of High Sierra?

Could this be a problem with the sound card of the new iMac versus the older MBP?

Since discovering the problem I have re-loaded the project in my MBP and it plays all clips sound perfectly.

Any tips on solutions would be much appreciated.

Could be a High Sierra issue with that iMac, too. FCPX 10.3 isn't 100% compatible with HS. Waiting on 10.4 "sometime this year" to make it so.

Not sure I've ever worked with .mts clips in FCPX, so beyond that, I dunno, but others will.