O/T ... engine noise question?

I hope you'll forgive the O/T post as I appreciate this isn't a Honda question. However I've often had good advice from here and it's really an engine issue rather than anything car specific! And I still have an ATR as
the main car ;o)
I'm thinking of buying a UK spec Focus 2.0 Ghia (5 door, petrol, manual, 2001 reg). I took it for a test drive today. Starting engine from cold, all sounded well enough and the car felt solid on the road. However there was a strange engine noise below about 2500rpm that has me a little worried. I can best describe it as like demented pinking (but not pinking)! It's quite noticeable and happens in any gear, but obviously you hear it more in 3rd/4th as you can keep the revs there (needs some throttle to make it happen - dies down at constant revs).
The car has been off the road for almost 6 months, so probably has yucky deposits at the bottom of both the petrol and the oil. They're offering to do a mini-service and MOT for free. The service would include changing the oil and filter, flushing the oil out and the fuel system with a cleaning solution. They say they'll remedy any faults (it will have to pass the MOT anyway) and give a 3 month warranty on major problems.
Unfortunately I only got to speak to their sales guy and not one of their mechanics and he didn't know what the noise was. Do any of you have any idea at all what it might be? The car has some nice extras in it that you don't often see and is in good condition otherwise so it would be a little bit of a shame to let it go, but not the end of the world!
a
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Sounds like pinging..Could be many reasons. Anything from low octane, to improper timing, to overheating. I'd probably pass on the car myself. But if you bought it, I would let them flush the fuel system, but *not* the oil system. 6 months is really not enough time to degrade fuel too much, and the oil is not going to be any problem. All they need to do is change the oil and filter. They need to find out what the *real* problem is before I would even consider buying that car. MK
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I found this when browsing around and it sounds a lot like what I experienced:
http://forums.focaljet.com/zetec-tuning/420335-low-rpm-2000-engine-noise.html
It's a strange one. I'd have thought improper timing would have been constant across the rev range? Overheating wouldn't be the issue as it did it right from cold until I came back with it hot. Why not flush the oil system btw?
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al wrote:

If you're serious about purchasing the car, then it would be worthwhile to get a prepurchase inspection performed by an independent mechanic. If the seller won't let you do this, then walk away from the deal. Even so, why start out with a car with a problem unless the price is significantly lower than other comparable cars?
Eric
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