If you listen closely in a completely silent area with the PDA right up to your ear you can usually hear a high-pitched noise, but it's very faint. If you can hear it during normal use when it's a good two feet from your ear then there's something wrong. Has it been dropped, shaken, etc recently? Something could have been knocked loose in it.
I have (as you can prob tell) a Palm Tungsten E2 and have had it for about six months. Within the past couple days, I have heard this strange high-pitched buzzing/ hissing noise heard only if it facing towards you. I turn it over and put my ear up to the back and hear buzzing also. Is this normal for a PDA to become "louder" after a couple months of use? Its kind of annoying and would prefer not to have it.