Tinny rattle coming from exhaust area

[Conquistador]

For the past few weeks on cold starts in the mornings I've been hearing a metallic rattle coming from the back of the car. It only seems to happen on cold starts and if I pull away slowly. Once the engine and exhaust is warmed up, I don't seem to hear it. It doesn't get faster or louder as the car accelerates, so it's nothing rotational, just maybe something loose and vibrating.

I assume it's the exhaust because I put the suspension in 'lift' mode, started the car then shot round to the back and stuck my head underneath to try and hear where the rattle is coming from but didn't have much luck! It sounds like it might be coming from just before the rear silencers but I can't be sure.

Anybody have any ideas?