I've been trying to use some boolean modeling techiques but have been having problems rendering boolean subtractions. It appears there are noisy artifacts in the area of a boolean subtraction. I'm looking for help in figuring out how to fix this.

Here's a very simple sample. Create the letter A with a round bevel. Subtract a box from one of the legs. Render with ULTRA setting and you still have noise in the area of the leg.

Thanks in advance for any ideas or help how to fix.