Wife came home from driving the car saying there is a rattle that needs looking at, I'd driven it earlier and all seemed OK so didn't do anything. Yesterday she was doing the school run and in her words 'there is a terrible noise, I can't drive it, sounds like the exhaust has dropped off' so she left the car at her brothers house and came home. Called out the breakdown people and within an hour they were there, he was not allowed to test drive the car so my brother in law drove it up and down their drive while he listened. Fairly quickly diagnosed that a stone had become trapped on the engine undertray and was rubbing against the drive shafts presumably.

Quite a good sized stone, he said there is a little damage to the undertray but otherwise all OK.

I've come across stones trapped in the brake system before but nothing like this.

How odd. Did the break down man get it out? 

15 minutes ago, Steve Q said:

How odd. Did the break down man get it out? 

Yes he showed it to my brother in law, he said around big marble size! It all ties up from what my wife said , below 20mph still there but quieter, accelerate and it is diabolical. Quite where it was trapped I don't know but under acceleration and the engine moving in its mountings caused the 'orrible noises. Unfortunately I didn't get to speak with breakdown guy, I surmised the drive shaft or may one of the pulleys was catching?

Oh wow! Glad that's all it was 👍

How on earth did a stone that size get onto the undertray? Had she been off-roading?

Def no off roading, there has been some road gritting locally but the stone sounded much bigger, (pity  it  wasn't kept). As an aside I had the A/C re-gassed later the same day which did not fix the A/C not working well, so the car goes in next Wednesday and I'll ask him to have a good look underneath.