The Dev Team have released a minor update to their Redsn0w jailbreak, aimed at fixing lingering issues with the boot animation.The steps for jailbreaking your device with Redsn0w 0.9.6rc12 have not changed so you can use the guide posted here.
Users who rely on a carrier unlock, please note that you need to stay away from jailbreaking your device for now. Ultrasn0w unlock tool still doesn't work on iOS 4.3.1.
Those who have already jailbroken on iOS 4.3.1 using Redsn0wrc9/rc10/rc11 simply need to rerun the jailbreak and select 'Allow boot animation' option when available. Also please make sure you uncheck 'Install Cydia' option to avoid conflicts with existing jailbreak.
Download RedSn0w 0.9.6rc12 for Windows | Mac