Anyway, I know the song you are referring to but IDK the name of it offhand, so I went where I always do for OC songs I want to check out. I checked out http://musicfromtheoc.com/weekly_mix_season3.html and it doesnt have it listed at the top under 'The Aftermath'. You can try the first song listed but I dont think thats it. Theres only 2 more options I can think of:
1. The one I think it is the most is that the song you are looking for is a song that they created themselves rather than an actual song, sort of like the ending credits and the little scores they have in between scenes sometimes.
2. The only other option I can come up with is that I havent seen s3 in a while but Im almost positive the song is the same song they play when Seth is in TNG and it goes up in flames at the end of 'The Man of the Year' and they have songs listed there for those too. So you can try that. Either "The Pinoeers"- Tuung or "The Pioneers"- Bloc Party. Check out the link I sent you and look towards the top if you want to see for yourself.
If neither of those songs are them, then I dont know what else it could be and its most likely made up. Sorry. I hope this helps!