Well, if you're gonna open it.Hey esub.
Sorry, I've been gone for almost a week. Just got back to the forum to see what's up. The whistling sound is probably the sound another fan that can be reached by removing the keyboard. I just did a mod to my 8890 (thanks to Aussie) by putting a piece of thin foam between that fan and the motherboard for padding. The sound is actually that of resonation between the fan and the metal posts that hold the fan to the board.
If you are gonna open up your 8890 and give it some Arctic Silver 5, then I recommend that you do this mod as well. You can find more about it here: http://notebookforums.com/showthread.php?t=11150