This is a pretty unusual behavior. Do you hear the same artifacts in the audio portion of your stream when you are using Watch on Slingbox.com with the same Slingbox on the same network?
We also recommend you to check if your Slingbox is running on its latest software version (Slingbox PRO-HD is v2.1.350). Make sure to reply to this post with this information, please.
I have the same problem with digital distorsion in audio sound when watching on iPad on my 802.11n network with full signal strength. I don't have these audio problems when watching on my macbook pro using the browser.
Slingbox ID: 71FF06CBB3A8C043A2B5AE0D7E8EB4EA
Slingbox Software Version: 2.1.350
I've reported this a few times, my issue is still unresolved, even after replacing the hardware as recommended by support, case 00417941
It even does it using the inbuilt tuner so its nothing to do with my PVR.