I thought my iphone was so well made that it didn't affect any speakers with loud noises or buzzes like other cell phones.
However, ever since I synced my phone with PC's itune, so that I could get some movie files on to it, it started to affect speakers like my old TREO 680.
I am quite sure it has to do with the sync, however irrelevant it may seem. And apprently, one http://www.macosxhints.com/article.php?story=20071231014727222 proved that I'm not alone.
The aluminum foil method seems to work, but I would really like to know what itune/sync/ipod is doing to my iphone's shielding ability.