Last week I put some new phils on my commuter. I decided to continue the splurge with some sugino 75's and a Zen chainring. I got everything together and I am now noticing that my chain purrs louder at one position in my stroke. With further inspection I notice that my chain tightness varies through a full stroke.
Just this morning I rotated my chainring to try to verify that it was the chainring. After my morning commute of 6 miles, I still think it's the chainring (it was louder at a different and anticipated part of my stroke). I was riding hard and may not have spared enough attention to it, so I am going to take a cruise at lunch to be sure.
Is it common for these chainrings to be a slightly untrue? If so, why spend the extra money?