Fan motor buzzing sound coming from speaker on Inspiron E1705

I've searched the forum and haven't found this one ... my Inspiron E1705 is several years old, and in the last 6 months has started emitting a very annoying sound from the vicinity of the "grille" on the right side of the base - on the top - just to the right of the backspace key. I think this is a cooling vent, but not certain. It sounds like a small fan that is barely hitting on something under the top cover. I can give it a sharp rap with a finger and it will slow down or stop temporarily, but within a minute or so comes right back.

Any thoughts? And if you have a suggestion for "popping the hood" and checking underneath, I'm more than willing to do that, but don't know how to get to the inside ... any step by step instructions? I sure don't want to send it back to Dell - that's a minimum of $150 or more!

Your help / thoughts are greatly appreciated!

Just to be clear - it's not from speakers or sound card or anything like that - it's clearly from the right "vent" on the top of the base.

Thanks!

LES