Interesting... I hear a rattle, or a 'gurgle' noise as you say, sometimes. I find this usually happens in 5th around 38mph and somewhere in the 40's and 50's as well.
I brought my car into the dealer and they said my heat shield was broken behind the glove box - they fixed it under warranty. The noise went away, but now it's back so I dunno
Could this be an issue with the heat shields breaking?