Sounds like it.
Try going into Options--Audio, then go to the Drivers Tab and switch it to WDM, and turn the dithering to none. Then close out of it and Sonar and start it back up. It should do the wave profiler and check for the best settings.
Note: Sonar Producer is a very powerful piece of software and does not like to play nice with onboard sound cards. And on a further note: anyone who is going to pay $500.00 for Sonar Pro. should at the very least have an entry level recording card like:
M-audio 2496
E-MU 0404
Behringer FCA-202
M-Audio Delta 44
These have more sophisticated drivers than any onboard card, and will interface a lot better with sonar. Just my 2 Cents.