I think I know exactly which tune you are talking about, I just dont know what itīs called :/ If it got a name at all.
Itīs probably one of those small tunes that has been made specially for the show and therefore can be impossible to pick up anywhere.
Like my favorite tune from the show..I had no idea what it was..so I asked in this forum and people told me that apparently itīs called "The silly Brothers theme" and is made by Lenneartz Motifs, again....made specially for the show and hard to find. Itīs this small bass tune that we hear several times, love it.
They gave me this link:http://www.supernaturalwiki.com/index.php?...Original_Score)
You can take a look at it but I searched for youīre tune too at that page and couldnīt find it.