| CloudCobra |
You can't trade it away, but there are ways to hide it:
1) A ring of nondetection;
2) Cast Undetectable Alignment on yourself;
3) Take up to 2 levels in the Master Spy PRC;
If you don't play a Paladin, you can, however, gain the Aura of Good feature by taking an Exalted feat from D&D 3.5.
Otherwise, I do remember that if you trade in your Paladin levels for Blackguard PRC levels (from the Dungeon Master's Guide 3.5) it becomes aura of evil.