@Patrick your problem is different than the one above. If you closely read his thread he is getting chorus. I would not want others to think their is a common board design issue by suggesting it is the same problem.
If you have an audio probe it could lead you to the area with the problem rather quickly.
Also he has a verified source for his MN3007 and since he does get chorus through part of the rotation I would have to still ask where did you get your MN3007 chip? I have no longer been able to find “real” chips on eBay for well over two years now.
I have hundreds in my possession from 10 or more retailers and all are Fake. I only kept them so I could potentially recognize the “Fake Stamps” on them. Testing proved also that none of them worked at all in a verified working circuit. I always left bad feedback for reference. The feedback I left would be at least 1 year old by now and many even older. I had to quit trying at that point. Small Bear have “REAL” MN3007 chips – 80 left: http://www.smallbear-electronics.mybigcommerce.com/ic-mn3007/
Make sure both grounds are hooked up per the document which is another common error. The board has two isolated planes for noise reduction.