Hello! I use Sonar X1 (64bit).
I have a problem using mp3-encoders in Sonar. I tried the lame-encoder and Aaron's patch mp3.
There is no problem using the encoders, but the results sound terrible.
There is a electronic sound/overtone in the background, and the sound of the recording itself gets an electronic touch.
I tried to export Sonar-recordings as wav-file and transformed them with audiograbber in mp3. Absolutely no problem, good sound (Only restriction: wav has to be 16bit, more is not possible).
 
What is the problem with the other mp3-encoders in direct use in Sonar X1?
I tried several settings (16, 24, 32bit; 48 000 / 44 100 KHz). Every time the same problem... :-(

Per other posts on the matter, folks have suggested making sure you leave a little room at the top when planning to encode to MP3.
 
Additionally, make sure your conversion rate is set to 320, to keep quality as high as possible.
 
Please note that any conversion to MP3 will cause loss of data - that's a natural consequence of conversion to MP3.
 
I have issues such as you report when I export my audio to MP3 - I hope the above helps.  
 
Also, please note that I never produce MP3 for release where the MP3 was created as a direct export from Sonar.  I ALWAYS export as .wav and convert seperately.  I use MP3's from direct export from Sonar only when emailing scratch copies of works in progress for other musicians to hear arrangements, NOT for audio quality.  I recommend you too move your MP3 conversion downstream from Sonar - it's what works best for me.
 
Bob Bone
 

"Additionally, make sure your conversion rate is set to 320, to keep quality as high as possible."
 
Unfortunately, it does not work. There are the same sound-problems as with 128. :-(
There must be another cause.