That turned out to be the exhaust on mine
Mine does this and has done for a while. It sounds like someone is giving something on the rear a good tap with a hammer over bumps and dips in the road - even very small ones...
Any other thoughts would be welcome,
Another vote for exhaust. It may be hitting the underside of the floor. There are usually rubber bumpers on the underside (above the exhaust) of heat shields etc. When the box was replaced, it's possible one or more was dislodged. Or, in a related vein, someone noticed a missing/broken hanger, replaced it, and now exhaust sits higher and, coupled with the aforementioned hypothetically missing bumper, is hitting the underbody... My neighbour's car had exhaust bits replaced recently, and apparently the sections didn't quite align, and the pipework is just that little bit
skewed... and it does exactly as you describe.
It's worth a look!
If you can play a guitar and harmonica at the same time, like Bob Dylan or Neil Young, you're a genius. But make that extra bit of effort and strap some cymbals to your knees, suddenly people want to get the hell away from you.
- Rich Hall
Gone but not forgotten - 164 2.0, 164 Super 3.0 V6, 156 1.6 T.Spark, 156 2.5 V6...