PC Fans

Hey guys,
Last week or so, I've been getting a strange rattiling sound from my PC so I took a gander at it's in-sides and I've narrowed it down to the fan. It's kinda old, about 3yrs. to be exact. Now here are my questions...

1)Fix it or replace? I found this one site that said it could be fixed with oil, is this true? (link: http://insight.zdnet.co.uk/hardware/chips/0,39020436,2135514,00.htm)
2)How do I know what size fan I need?
3)Will if fit into the clip openings my current one uses? (no screws are used in my current one)
4)Most fans nowadays come with heatsinks, do I need to replace that with the fan?

Thank in advance guys!

before i answer, i will bring to attention the possibility of a loose power cable or somesuch in your case making physical contact with the fan blade.  makes a hell of a racket, but you just need to move the cable out of the way to fix it.

assuming the problem is actually the fan, though, on to the questions:
1) i'd recommend replace.  fans are cheap if you're not going for high-end stuff.
2) take old fan to computer store.  say "i want one of these.".
3) see 2)
4) if the heatsink is physically attached to the fan and can't be removed, yes.  otherwise, probably not.

Ok, Thanks for the quick response and as far as I can tell, nothing is hitting it(?)

BTW, I frgt to mention that the noise is only made when PC is starting up from a cold boot. It diminishes down to its usual self after a few minutes and if I restart it right after shutting down, it is still no heard. Again, it is only heard from a cold boot.

Oh, I'm not going for high-end (on a budget!)and it's not attached to the heatsink.