Possible DMF failing, water pump, cambelt idler, alternator, aircon pump etc, you could isolate auxilliary belt driven driven items by removing the belt the night before and then doing a cold start with it off.

No need to go into any possible engine problems, there is reading enough on this site alone to keep you going tll the new year.

Edited by gordonbennet on 13/12/2016 at 11:06

Got an update on this for you. Just so you know the car has done 113,000 miles, and I'm pretty sure it has the orginal turbo.

I'm pretty sure the rattling sound isn't anything to do with the DMF. I drove the car to our local petrol station, and whilst waiting to fill up the car was making the rattling sound. I put the clutch in and the car still made the rattling sound. When I got it back home the noise had stopped. The noise seems to be more noticeable while idling, and not when driving or under load. It doesn't lack any power, still pulls really well, so I'm not convinced its the turbo. I did check the the spindle in the turbo when I took the air intake pipes off to do an air filter changed not long ago, and there was no movement in the spindle, and it spun smoothly and freely when I turned it.

Before I went out this morning, I took the auxiliary drive belt off and started the car from cold, and no noise occurred at all. For its first MOT of me owning it, I let my mechanic mate give it a pre MOT, and he noticed that there seemed to be dust coming from the crankshaft pulley, didn't know if this was significant, but its been like it for many miles now and not caused any problems.

The sound to me does seem like a metallic rattling sound that is in time with engine revs.

Any other ideas would be greatly appreciated.

I agree with your comment about the crankshaft pulley, I've been worried about it since he mentioned it. However we are real good mates, and he has always told me not to worry, the worst case scenario would be fitting a new engine, which he would be able to source and fit for me. He's also pretty relaxed about paying him for jobs, accepting bits here and there when I can afford it. I've now driven the car at least 8000 miles since this was mentioned, and I'm pretty sure the rattling I've been getting recently isn't linked to the crankshaft as the noise seems to be coming more from the top of the engine.

I also mentioned the noise to him, and let him listen to a recording of it that I took on my phone, and he seems to think it sounds like the auxiliary drive belt tensioner is on its way out. I had to record it for him, as I can't always guarantee the car will make the sound when he's around. I have to say he has always been pretty spot on with diagnosing any problems I've had in the past with various cars, and he's worked on plenty of Focus' so I'm hoping this is the issue. He did also mention small timing chain tensioner failure too, but seemed to think this was less likely. He's going to give it a good look over soon, so hopefully we can get to the bottom of it.

Cheers for the comments, I do appreciate the input from all.

And thanks for the update, an example to those who never return once advice has been given to say whether any of it worked.