S40 (New) Brakes : Incessant rattling!

[RollingThunder]

I think I know the answer to this one, but before I spend any money I wanted to sanity check my thoughts with you... thanks for humouring me

Since buying my 2008 MY S40 D5 a month ago, it has had a rattle under the back end. I thought it was an exhaust heatshield, maybe an exhaust baffle, however the noise went away as soon as I touched the brakes - so that would seem to point to the anti-rattle shims in the rear brakes?

I put the car up on ramps at the weekend and couldn't find anything loose that could account for the noise, so I took the wheels off -and everything seems ok. The caliper springs are in place and providing tension etc, the pads aren't loose fitting (the handbrake was off!), and the calipers etc are securely mounted. So all seems well, but I am still tempted to replace the pads, because I didn't remove them to inspect them (time constraints) so they may still be missing the 'prongs' that fit into the pistons?

I couldn't think of anything else that would cause the rattle, especially with it ceasing as soon as I touched the brake pedal...

Am I missing anything that you can think of?

Many thanks
RT