Can't remember exactly which ones they are, but, you need to go to the Jointed Rail webby - http://jointedrail.com/
They are either cab interiors, or, engine sounds, probably for TS12, you may need to open an account, it's free, to gain access to all of their goodies.
based on both of those... I think I came across it from a download on Jointed Rail, is this a bogey or something? try looking at that missing dependency in content creator plus it shows me what it belongs to. Well other than that good luck finding it =/
-Bryan
