Did you try http://forum.cakewalk.com/FindPost/2900972

Yes, this was apparently posted while I was typing my post.  This worked and all is well.  Thank you so much...
R 

I have the same problem, no audio metronome on the dropdown list.
here is my solution,hope it work
1. instal sonar old version,i try to instal sonar 8 first
2. uninstal sonar 8
3. instal sonar x3
4. copy audio metronome folder from old sonar folder example C:\username\AppData\Roaming\Cakewalk\SONAR 8 Producer Edition\Metronome
5. copy the audio metronome into C:\username\AppData\Roaming\Cakewalk\SONAR X3 Producer
6. done, now open your sonar x3,and metronome is solved
 

It also worked for me, thank you so much...

i had the same problem fellas but i read your way to scook and that worked for me. thanks again so much