Extracted from the above mentioned statement:
CloneDVD does not touch the sound during the encoding process due to license issue.
-> "Applying any filters i.e. normalisation or reduce output gain" would "touch" the sound!
Ok, I did make an additional test: extracted the DD 5.1 audio stream from the Original-DVD and from the DVD-Copy for a checksum-test. The files are the same! The sound isn't touched, as expected...
So, just a possible assumption:
Could it be that you are hearing different sound streams with your DVD-Player (Original-DVD: DTS; DVD-Copy: DD 5.1)?
Please check the default settings in your DVD-Player.
And maybe Olli can say more about this issue...