MacBook - Macbook fan issue?

Hey everyone. I am having some weird fan issues that I'm hoping someone can diagnose. When my white 2.0 ghz c2d, 4gb ram, x3100, Leopard Macbook is sitting with nothing running, the fans will randomly rev up to 6000 rpm (according to istat). My Macbok is no longer under the one year warranty and I did not purchase Applecare. Some past history:

1) I've reinstalled Leopard once or twice, although not within the past year.
2) I've reset the SMC fan control twice, if not three times. Things got better after the first time, but have since returned to the usual problems.
3) The plastic cover around the keyboard is cracked all over the place. I'm going to get it replaced, but it's been like this for a long time. Could this create weird air circulation and make the fans go crazy?
4) I have turned gmail notification off on startup (nor do I run it anymore). I found that turning it off actually reduced the fans from revving.
5) The fans definitely turn on when my battery is at 99% charge, which is something that originally led me to reset the SMC the first time.
6) I am still running on my original battery and AC adapter. iStat shows my battery at 99% health, although it has been lower at times - I don't remember if i've completely drained / recharged my battery lately (which would have helped repair it), but it has gotten down to reserve power numerous times. It's fully charged right now.
7) I'm upgrading to Snow Leopard soon but hoped to solve this issue beforehand.

Do you think this could be a faulty battery or power supply? My fans turn on when nothing is running but Safari, Growl and Microsoft keyboard and mouse helper (I use a wireless microsoft keyboard and mouse set when I use my external monitor - I assume the helpers are drivers and not actual help documents...).

Thanks for any and all help!