Ideas

[tempest]

unfortunately it's in the nature of that particular sound that it's got deep bass and little upper frequencies to "cut through" other sounds

Yeah, you're probably right. Didn't think of that, I just chose it because it appeared a little louder than the one Cleaner suggested.
That's what happens when a noob dabbles at sound engineering ;)

But yeah, give it a try.
The one I used: http://www.freesound.org/samplesViewSingle.php?id=22416
Cleaner's: http://www.freesound.org/samplesViewSingle.php?id=32731