www.makemkv.com

There's a program called MediaInfo that can show you a lot of details about your media files. It can easily be installed via Homebrew on your Mac if that's your thing. That can tell you if there's actually an audio track in the .mkv file MakeMKV produced and the format it is in. Then we can know if there's something wrong with the rip or with the playback setup.

+1 for MediaInfo, I couldn't live without it!

Also, let us know what you're using to play the mkv file with. It's quite possibly a codec issue (as in, your player doesn't have the necessary audio codec installed)?