Wow, there seem to be a LOT of threads with these hi-freq oscillation problems lately. As I mentioned in a different thread, when you hear squeals and whistles, I think that's often a case of the internal op-amps being fed a lot of signal outside the regular audible range. A lot of these opamps can operate way outside of human hearing, but when you overdrive them with a signal at 40KHz it has odd detrimental effects on the part of the audio spectrum we can hear.
This stuff is almost certainly emissions coming through the air. Just a couple of other thoughts - is this with wireless transmitters? Are people experiencing these problems away from notebooks, PCs, LCD monitors? Is there a cell phone in your pocket while you hear these problems (if you hear a quick and quiet burst of static every second or so, that's the cell phone you left in your pocket). I wonder about whether there are byproducts from Wi-Fi access points as well.
The really interesting test would be to see if these problems go away if the high frequency response fed to the opamps was limited to no higher than 10KHz or so, maybe even less. I don't know whether this is the factory's RF mod or not.
David Fung
