I understand that your getting an echoing/metallic sound while watching your Slingbox PRO-HD from you IPhone and IPad. I'm sure that can be frustrating. I have an article that will provide you with some basic audio troubleshooting. Slingbox Audio issues: Basic Troubleshooting .
Hope this helps.
Sling Moderation Team
I too have exactly the same issue.
On the iPhone I get the echoing you've described, which for the technically minded sounds a lot like quantisation noise.
I also get it if I use the standalone app for Mac (which I don't anymore since I discovered the brilliant Fluid that allows you to create a standalone applicaion from a webpage - but I digress).
I don't get it when using the browser based app.
I have the Slingbox PRO-HD.
I've tried several different A/V sources (HD & SD) - this has no effect.
I still get the effect when my PVR is paused (sending no audio).
<rant>It's really annoying but I don't suspect that it will get fixed any time soon. Sling have shown over a number of years of woeful support that they don't really care about consumers or end users. They are too focused on trying licence thier technology to manufacturers and avoid getting sued by media owners to even have a few coders improve thier apps.
The controls on the iPhone app are still dreadful and it has not been updated for 6 months!!! No app is that good. </rant>
Please Mr polite man who is paid to monitor the forums and placte the users, tell your overlords to refocus some of thier resorces.
The only reason people still buy Sling is there is no credible alterative.
Knicks this issue is not going to be resolved. I don't hear it on my WDTV Hub Slingplayer - but it is there on Sony Experia Tab, Samsung Galaxy S4 and Apple iPhone 4.
This is a hardware fault as the App could have been fixed by now. It is well known to Sling but they do not have a fix for it and they refuse to engage with any meaningful solutions to it here in this Forum.