Hopefully i can help..
Does the knocking seem to happen on smoother roads too ?
Are all the supports on the exhaust system as far as you can tell all intact?
Hi, sorry for the delay. The exhaust itself seems ok, but the mesh metal, (is this the heatshield?) is loose above it.
The sound just seems too regular for this to be it.
I'm going out to drive it with a rag above the exhaust for a short distance, and I'll get back to you,
Hi..there thanks for your reply..
There will be heat deflection shield between the exhaust system and the underside body of the car,all cars have these it just to deflect the heat..sometimes these can often work loose due to corrosion mostly etc..sometimes you can manage to bend it away so it does come into contact with anything or try removing the fixing that holds the sheild section if it come away from one and put a larger washer etc in place or remove it totally - As long as the rags in place for very short time round the block just to diagnose..the only other thing could be possible suspension wear on the back if this crops up more often over rough road surfaces..also check the rear wheel nuts are secure aswell as jack up each side one at a time and feel for any play movement just to rule out possible wheel bearing wear on the back..maybe spin each wheel in turn obviously chock the front the wheels and put into gear as you need the handbrake off to do so and see if you hear anything..I do hope this helps
Thanks Robert. The h/s is loose, but I can hear it as a separate noise. Wheel nuts are secure, so I drove again with a back seat passenger. She says the noise seems evenly spread at the back.
Robert I'm going to my (in my experience) very reputable garage tomorrow, so wish me luck.
I realise that it's difficult diagnosing noises by email, but I appreciate your time, and I'll click to ensure you get your credit.