I don't like the sound of this (at all...)
 

Just been out for a short jaunt and, immediately after a bit of a hop over a lump in the road, my engine has started making the most appaling racket.

Sounds like a ropey old diesel engine idling, but much much louder. The sound rises and falls with revs. Imagine someone sticking a large twig or a screwdriver blade into the fan and you'll get the idea.There's absolutely nothing visibly wrong, at the roadside, and the engine runs and performs totally normally. But what a din!

It doesn't sound like an exhaust problem but if (as I fear) it's bearings, wouldn't there be some other symptoms (or a little warning) and would it happen so instantaneously?

:(

Yikes! That's the sound of money leaving your wallet. I have no idea what that might be, John, but I hope its something other than bearings. $$$$$

Hope its a happy ending, J. Doesn't sound at all promising, though, I would agree..

I guess looking at some of the advice from the semi recent thread when pesty's car suddenly went all noisy, broke its big end bearings, might be a good start: I suppose I would be desperate to drop the oil to see if theres chunks of metal coming out, but maybe best to get it to the specialist before doing all of that.

Or maybe this is your opportunity to fit Motec or a supercharger at last!

Good luck, got my fingers crossed..

John:

Sorry to hear about this. If you spun a bearing, the noise would come on rather suddenly. For sure look for other less expensive problems before pulling the engine. Ideas:

broken chain tensioner
distributor (not sure this could get that loud)
alternator (bad bearing, broken rotor)
power steering pump

Good luck. This is not a nice Christmas surprise.

John... I'm thinking something has fallen into the space between the fan and the alternator. I can't imagine a bearing going bad because of a bump in the road. It is tied to engine revs and NOT speed, yes?

Imagine an old tin/aluminum rubbish can with a length of heavy chain inside. If you grabbed the end of the chain and dragged it out of the rubbish can, over the edge - might it sound like that? If so the last time I heard it was the result of a failed chain tensioner on a 2.7L motor.

Not nearly as expensive as bearings if it turns out to be the root cause. Luck to you Sir.

RallyDog,

I guess it could be described that way.

Here's hoping...

Remove the fan belt, see it the noise continues, go from there.

Hiya John Boggiano
An oil test will tell you if its bearings . I would not run the motor at all until it is fixed .

I agree with Indycam, I wouldn't want to run this untill I was 100% sure of the cause, to much to lose JB.
Oil samples, and making sure nothing is obviously externally loose would be my starting points

kevin

John, this sounds like the noise I had earlier this year, I hope not as it was bearing #3. OUCH

It's in any case an eyewatering sound so close to Christmas. Hope it turns out ok.

Hi John,

If I were you I'd start with simple things like something interfering with the fan or belts, before worrying about the big stuff. You say you noticed no difference in performance, and this intuitively makes me think the problem isn't as big as you may be thinking.
Good luck mate, and have a good Christmas.

Craig

Tough luck JB, hope you get it sorted.

JH

Have you tried turning the engine over using a wrench on the alternator fan to locate the noise? If you have a stethoscope you should be able to narrow down the exact location.