Strange rattle (rotating?) noise when accelerating from a stop

[Conzo97]

I've started noticing that intermittently there will be a strange rattle-like noise from underneath the car for about 2 seconds when accelerating from a stop. I cant hear it after this - only when accelerating from a stop. It's possibly worse when more people are in the car. I also notice that there's a clunk in the rear suspension going over bumps when I have someone in one of the back seats. I don't know if this is a separate issue? It sounds quite minor but at least the rattle noise is hella annoying.

It's a 2010 Omega wagon

If anyone knows what this may be, I'd be very appreciative.

 

[Fu Manchu]

Timing chains loose.
An exhaust component loose.
Worn bushes in the rear.
Buggered (or nearly buggered) catalytic converter/s.

 

[gossie]

Have you been UNDER the car and LOOKED?