You know if you move your phone near a PC with speakers, you hear that crackle/squelch... I wonder if this is a bad design in the speaker/cable - unsheilded. This simply should NOT happen and there will be no "PATCH" as it's not software if it's this !
Mine still does it on Airplane mode. I don't think this is an issue related to interference but rather the phone is actually producing the sound. Most likely a software issue as it only happens with certain sounds and does not happen in vibrate mode.
This is a different issue than the "GSM buzz" interference that TDMA-GSM phones cause with various electronic gear, that francisc mentioned. The short high pitched sound emitted by the 3G S is unrelated.
I hate to say it but this issue is triggered by EVERY system sound you make, even a keystroke! The sound last approx. 3-4 secs after the system sound has finished and happens with all cell and data features off.
I hear it after locking, unlocking and after email alerts. I don't hear it after keyboard clicks. I haven't noticed it after SMS alerts or call ring tones, but haven't listened for them yet - I have to put the speaker near my ears to hear it at all.
Ya, keyboard clicks and certain others like unlocking seem to have a higher frequency and are harder to hear and sound more like static to humans. It's not really distracting unless you're in a really quit room, I just thought it was weird that my dog came running everytime I sent a text.