A mod I made back in TTW 2.9 that I never ended up releasing, this is a simple change that will swap out various sounds for the ones that originally played in Fallout 3, such as the iconic 'Ka-ching' when earning XP, and the old quest sounds.
They will change between the New Vegas and Fallout 3 versions depending on which wasteland you visit.

These sounds are currently switched based on your wasteland:
Quest Added
Quest Updated
Quest Completed
XP Earned
Level Up music.

Also, seeing as Fallout 3 didn't have a sound for discovering a location (And it was just a message in the corner), this mod disables that when in The Capital Wasteland.
Can be re-enabled by typing 'set DisableDCLocationSound to 0' in the console and restarting your game.
Part of the reason for disabling it is that, in NV, the 'Location Discovered' sound is shared with the 'Quest Added' sound.

As a bonus that I didn't realize was a bonus, this makes use of the 'Quest Updated' sound in Fallout 3, which apparently never played in the original game.

Planned Features:
An option to make the sounds stay as NV's after travelling there once, but I just wanted this out there finally.
The option to make the Location Discovered sound always be NV's one, rather than disabling it outright in DC.