Strange Rattle/Clunk

[madcowbeavis]

So, I've noticed this since I bought the car a year ago, it never bothered me because once the stereo gets past about 25 you can't hear it anymore, but actually talking to people in the car with the stereo past 25 is

When I'm coasting down the hills here or on relatively flat roads (READ: No power or brakes applied, car in Drive), there is this very annoying clunking sound coming from what sounds like the back end. I've never heard it coasting uphill (I get lazy when it comes to breaking for corners...), which makes me think it's a worn fit or a busted bearing somewhere (weight of the car/gravity pushing on the drive-train going up hill would seat the component back into place, hence why it only does it downhill, if theory is correct).

She's due for a service so I thought that I would try and get a heads up on what might be wrong. It's not the transmission as I've had that serviced since I've had it, I'm hoping it's not the suspension because I had all the bushes/shocks/struts replaced and 3 different companies looked it over. Which to me leaves a drive-shaft or diff issue, neither of which sound extremely appealing

Does anyone have the foggiest clue about what I'm talking about?

[cpbait]

could be a suspension bolt loose or a bearing issue, i have a clunk in mine and just found out recently from a performance place in Melbourne that my rear control arm/diff cradle bushes are ****ed, these are the big bushes at the end of the control arms where they connect near the body, and i only have it under certain conditions, $125 or so a pair that's one left and one right each side through peddars using peddars nolathane bushes.

hope this helps a bit, not sure what holden would charge if its them.