Reduced sound level for VOB files only

Hello all!
The first thing that I would like to know is about DVD Rom. What brand will you recommend? Secondly, I have got into a strange thing. I installed some DvD cutters and joiners, used them and then all VOB extension files started to give resuced sound than before. It was all going well with those before I used them in the cutters and joiners. Can anyone suggest me the procedure so I can get the previous level back again.
Thanks