Likely the fan noise is merely a coincidence, which of course may mean that your fan is about to die. However, is this a desktop or laptop? With Slackware installs on laptops, I've much more fan activity than while running Windows.
The 10-15 second delay before presentation of the login prompt is due to your system, or services on it, attempting to use your network interfaces, when they haven't yet been configured. If you set them up in /etc/rc.d/rc.inet1.conf, as Bruce suggested, this delay will be resolved.
Once you've done that and are comfortable with how that works, I recommend that you check Alien's page at:
...especially his modifications to "several of the Slackware rc scripts". You'll find them particularly helpful (brilliant, even) with your WiFi card/connection. Just to be sure to read his notes thoroughly, and then read them again, to make sure you understand what you're changing by implementing his enhancements. (And save backup copies of the distribution versions of the scripts, so you can just copy them back into place to restore functionality while you work with his versions of the scripts.)
slackbook.org is indeed still down, as of this writing (2/28/2008 8:30 pm PST)