The program will always record a fresh soundtrack each time you record, even if you are not recording dialog. I'm not sure what you mean by adding silence. Is it making the existing soundtrack longer?
I mean when I add a sound track, it ads a silend second or two at the end. So if the track say is 10 seconds, it makes it 11 or 12 seconds. It was not doing this before.
I must admit that I have not experienced this before and I'm not sure what to do. Have you tried trimming the excess audio in the timeline (see below). Also, do you know if this behavior occurs in an earlier build of the program?
Unfortunately, I cannot replicate this on my PC. If you haven't done so already, use the feedback feature in Character Animator to report this bug (see below). I know this isn't what you want to hear, but you will probably have to use one of the earlier builds until this bug gets addressed.