New rattle - timing chain
 

Started the car yesterday after it sat in the rain for four days. Sounded Ok for a mile, then I heard a light rattle start up. When the car is static and out of gear and I rev it up, the rattle rises with the revs, so it sounds like engine-related rather than clutch or gearbox. Funny thing is that it started suddenly. I have taken the car up to red-line a couple of times and it is running well. I can hear it clearly when listening under the back of the car when idling. The car has 48k miles on it, and always had frequent oil changes with Mobil1. Timing chain perhaps? Any other thoughts?

Take the engine access cover off and remove the belt. Start the engine and see if the noise is gone. If it is, the noise is probably one of your idler pulleys. Other possibilities include water pump, AC/alternator pulley bearings.

Thanks epapp. Yes, examining the belt pulleys would be my first diagnostic check. Having run the car a few more times the rattle does not happen immediately on startup, so hopefully not an IMS or timing belt problem. From reading other messages these seem to be more evident on startup.

I meant timing chain of course, not belt!!

Well the noise went away and all was fine for two weeks. Today I heard a screetching noise, the temp light came on almost immediately and then the engine shut down. I topped up the water reservoir after letting everything cool down, and the engine runs but the screetching is still there. There is also water dripping under the engine, so it sounds like the water pump has gone.
Just goes to show that if you hear an unusual noise, there is usually something about to fail!
Tow truck is on the way!

If you had taken the drive belt off, you would have easily found the sound to be the water pump before it failed!

:screeeeeeeech:

Yes, you are probably right, but we have been busy with house renovations the last two weeks, and some travel. And the noise had gone away!! I just hadn't had time.
My repair shop has confirmed the bad pump and a shredded belt, They will flush everything out before fitting the new pump, so hopefully everything will be OK after that. The motor had just reached 50,000 miles, so about time I guess.

You generally fail first before you succeed! Now you know ;)

This reminds me of a couple seasons ago, I was driving my car (60 mile commute back then) and when I pulled on the exit ramp I heard a load thump right behind me. This was followed by a few more loud thumps and then nothing. As I made the turn onto the main road, I noticed I had no more power steering so I knew what just happened. All I could think of is what component just died to make the belt snap. Managed to get it home without overheating it and the next day I peered into the service compartment. I had lost the idler pulley and not only did I find all the pieces of the pulley, but the belt was in perfect shape. Not a mark on it. Bought a new pulley and installed the old belt as that was the last drive before winter set in anyway and I was back in business.

Was the pump impeller intact when the pump was pulled off? If not, and you can't find all of the pieces, then some small ones could have travelled into the engine and got lodged there, particularly in the small passages in the heads. This could lead to local hot spots and possible head cracking. Backflushing MAY help to find the missing pieces, but is not easy.

If you remove the pump, and impeller blades are missing, you have a bigger problem. Those must be fetched, else you'll crack a head.