This post explains how you can fix the vibration issue of side switch after the jailbreak. A simple re-run of redsnow will solve the problem.
If you have already jailbroken your iPhone 4 and iPhone 3GS running on iOS 4.3.1 or above, you may have noticed a weird problem related to side switch vibration. Today iPhone Dev Team has released updated versions of both Redsn0w and PwnageTool to fix this issue.
How to Fix Side Switch Vibration Issue on Already Jailbroken iOS 4.3.3:
If you have already jailbroke your iPhone 4/iPhone 3GS with Redsnow or PwnageTool, simply re-run the Redsnow on existing jailbreak while selecting “Install Cydia” option.
How to Fix Side Switch Vibration Issue if You are running other than iOS 4.3.3:
If you don’t rely on unlock, update your device to latest iOS 4.3.3 via iTunes and then run the latest Redsnow to jailbreak it. But if you rely on unlock, use Pwnagetool 126.96.36.199 for cooking custom iOS firmware which also includes Side Switch Fix.
Download Redsnow 0.9.6 RC16 and PnwageTool 188.8.131.52