Hey there,
I stumble onto this thread via a Google search and had to respond. I'm a life long Trek fan (TOS, STNG, movies, etc...), and also a full time working musician based in Nashville TN. Please don't mis-read this post as an advertisement. But a few years back, I produced an audio CD titled Starship Ambience. Like a few have mentioned in this thread, I too was interested in having some sort of continuous background sound that suggested you were aboard a spaceship, traveling thru the galaxy.
I actually marketed my CD back in the 90s via ads in Sci Fi magazines. Sold a few 100, then kinda thru in the towel. I still have a few cases of shrink wrapped CDs. It's a very nice production, featuring 60 minutes of uninterrupted starship ambiance. It does have the rumble everyone has talked about. But for more interest, I chose to create the ambiance of a starship bridge. I would be happy to share a few copies of the CD with anyone who was interested. My business interest in selling the CD has pretty much dried up. Now, it would just be interesting to hear some feedback on the quality of the production.
There's a whole bunch of info, and sound bite at...
www.starshipambience.com
There's also a contact page there, if you'd like to email me directly about getting a copy.
Interesting topic!
--Robb