Knocking Noise from Engine Bay

Today a knocking noise started when driving. It comes from the engine bay and sounds like a metallic tapping noise, possibly from the top of the cylinders.

It's regular and it doesn't happen at all when sitting idle or when stationary even if revving the engine. It continues knocking when coasting in neutral and the knocking doesn't speed up or slow down while coasting in neutral and revving the engine. It does get a bit louder and faster when going quicker though and slows down as the car slows down.

I lifted the bonnet when I got home, can't see any fluids leaking anywhere and checked oil which is OK. When I tapped the engine cover it sounded very similar to the noise I could hear when driving which makes me think it's maybe a cylinder problem??

I'm rubbish with engines but would like to know what to expect to be the problem, and if I should keep driving it. I was going flat out for 10mins or so (6600rpm) about 20mins before the noise started.....

It's got new cam belt pulleys timing belt etc. The driveshaft has some play in it...dunno if it could just be something to do with that??

Answered! View the answer I have this problem too

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Is there any chance you can record the sound and may be post it somewhere? If it would be camshaft noise, valves or even more sinister things, the noise should respond to the engine revving....

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Hi, Really stupid thought. Since it doesn't happen idling when stationary or when revving the engine when stationary, but seems to follow the speed of the vehicle, you haven't got something lodged in a wheel by any chance, rubbing or knocking against something perhaps?

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even this "The driveshaft has some play in it."can make a knocking noise if the joint is wearing out...

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Hi Thanks for all your comments...unbelievably I found out what it was when it started on the motorway the other day. Autoglass recently replaced my windscreen and did their usual hi standard job...the rubber seal along the top has come loose!! The first day it was knocking on the top corner where it came loose so the sound was transferring down making it sound like the engine bay. I only sussed it when the noise got worse on my to a garage to get the problem fixed....it started banging on the roof and was clearly not engine!! The strip then came right off and is now up the m25 somewhere

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unbelievably I found out what it was when it started on the motorway the other day. Autoglass recently replaced my windscreen and did their usual hi standard job...the rubber seal along the top has come loose!! The first day it was knocking on the top corner where it came loose so the sound was transferring down making it sound like the engine bay. I only sussed it when the noise got worse on my to a garage to get the problem fixed....it started banging on the roof and was clearly not engine!! The strip then came right off and is now up the m25 somewhere

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It sounds as though you may have a bad CV axle. Most are fairly easy to replace.

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What are you doing going flat out for 10 minutes, trying to blow up your engine? Were you watching the engine temperature?

So it doesn't make the tapping noise while stopped with the engine running. Not very likely it's the engine then is it?

It does make the noise while you're coasting in neutral speeds up and slows down when you speed up or slow down. Sounds like drive train. I suspect the U joint on a drive axle. If so, the noise is usually louder when you are going around a tight turn. It's not a difficult fix. Lucky you, I hope.

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