Tom:
In response to your post, I'm assuming you are attempting to hear audio takes as they are recorded while looping.
When doing loop audio recording with the "Sound-on-Sound" record option set, you will only be able to hear the clips that exist when the transport is started. Audio clips that are being produced by each take while the transport is running will not be heard. Even though the documentation is ambiguous regarding this, here's what it says regarding having the "Sound-on-Sound" record option enabled:
The new material is merged with any existing material. This means that any existing clips on the track are left unchanged and all newly recorded material is stored in new clips. While recording, you will be able to hear material from existing clips.
You can find the above documentation here:
http://www.cakewalk.com/Documentation?product=SONAR X3&language=3&help=Recording.11.html#1071429
I asked this same question a few years ago, and after receiving several conflicting answers, "Susan G" kindly pointed the answer out in the documentation to help me. You can find that thread
here.
Hope this helps,
Paul