MP4 audio quality issues when output to SCORM

Folks

I'm having some audio issues with MP4 videos that are output to Scorm. 

The original screencasts are recorded in Camtasia and the audio quality on the MP4 file is perfect.  When I listened to the MP4 from within Articulate, it's perfect.  But when I output the file to SCORM, the audio is very tinny and it degrades for some reason.  All the rest of the MP3 audio on the slides is fine - it just seems to be the MP4 files.

I've tried to increase the audio bitrate to 128 when outputting from Articulate but it's still the same result.  Also, the audio bit rate when outputting the files from Camtasia is also 128 and as I say it's perfect.

I uploaded the file to Scormcloud and the audio issues are still there, so I'm not sure if that indicates the problem lies with the output through Articulate.

Has anyone had similar issues or has any suggestions as to what I can try to fix this?  I've been through other questions on this forum and have tried the above in response to that but it doesn't seem to be doing the job.

Thanks in advance for any help.

/D