DAC reclocking noise?

I'm increasingly listening to music streamed from my iMac G5 to an Airport Express using the optical output into a Marantz SR7200 AV receiver that has a built in DAC. I'm enjoying more of my music collection because of the convenience of iTunes and mostly content with the audio quality except for an annoying burst of noise at the end of tracks sometimes. After reading a thread on Audiogon where the issues of jitter inherent with using optical connections and the need for the DAC to reclock, I'm now wondering if the Marantz's DAC reclocks and burps noise? Or perhaps it's an issue with the AirTunes and the AXs' wireless connection?
The rude burping noise is tolerable now, but as I get older and grumpier I may have to take action. I'd appreciate any help with this issue.
I use the same setup of an iMac G5 to an Airport Express and then on to a Benchmark DAC via the optical connection. There's no extraneous noise of any kind so, at least in my setup, the issue isn't the G5 to Airport connection.