Which version of RioPlay are you using? I'm on 0.29a2 and have also noticed an intermittant low-level crackle on MP2 WF streams, although to be honest I hadn't pinned it down to one channel only. I also hadn't realised that the re-sample code had changed - thought I'd just grown accustomed to the sound! Will do some tests to see if it's only on the left channel.....

Also... do you get the problem whereby if you add other stations (Shoutcast streams) to an active stream and then inadvertantly scroll beyond the end of the stack your Receiver will lock solid, needing a cold re-boot?