Hi All

In need of someone's views, thoughts and advice regarding something that has been happening with my car lately.

When I accelerate hard at low revs in 4th or 5th gear, I get what can only be described as a flapping sound from the front drivers side area. The best way to describe the sound is like a piece of card hitting the spokes of a bicycle wheel as its going round. As I said it only happens at low revs in 4th or 5th under acceleration, as the revs increase it goes away, its not noticeable in any other gears either, and the loudness can be variable, quite loud sometimes, then sometimes hardly noticeable, but definitely there. I've checked obvious things like loose arch liners, engine under shield, serpentine belt, but nothing seems out of place and I'm sure if it were any of these types of issues it would happen all the time. No problems with the running of the car whilst this happens.

Any one know what could be causing this or what to look out for?

Any info would be greatly appreciated.

Hi there your possibly looking at a loose belt and it's slipping I would get a garage to check it for you and get codes read see if any show up

Cheers for the reply Damien

11 minutes ago, Damien said:

your possibly looking at a loose belt

I take it you mean alternator belt?

Yes mate 

Cool. I'll check it out. I think its due a change anyway, no idea how long its been on there.

Thanks mate.

Mines been doing this for 20k miles since I bought it.  Can't work out what the problem is but it's obviously nothing major.

I was worried about it being the turbo as it sounds like poking something in a fan but there's nothing in there and no play in it. 

Accelerating hard in low revs and a high gear is never a good idea anyway.

Possibly just the diesel knock being exacerbated by lugging the engine?

2 hours ago, TomsFocus said:

I was worried about it being the turbo as it sounds like poking something in a fan but there's nothing in there and no play in it.

Described the noise exactly the way I hear it. I've had to do some engine work recently and whilst doing it, had a bit of a look at the turbo, all seemed fine in there, nothing in it, no play and nothing loose.

2 hours ago, alexp999 said:

Accelerating hard in low revs and a high gear is never a good idea anyway.

I don't make a habit of accelerating hard in low revs and high gears, sometimes just happens before I realise. Surely if it was diesel knock then it would have happened every time I accelerated at low revs / high gear since owning the car? This flapping noise has literally only been happening during the last few journeys I have done in the car.

For the sake of a few notes, I'll change the alternator belt anyway and see if that cures it, car is due belt change anyway.

Not just that you have the window open recently? I have had that happen to me, only noticed it in warm weather because I had windows down.

2 hours ago, alexp999 said:

Not just that you have the window open recently?

I've always been one to drive with my window open slightly, I like fresh air when going along. The only time I drive with it closed is when it's freezing cold, raining or on dual carriageways and motorways (unless weather is boiling hot then I'll keep it open on these roads as well). I'm as sure as I can be that this noise is a new issue.

I often see this on cars, where the under engine tray is not secured, its like flying a kite under the car

Have you checked this?

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5 hours ago, jeebowhite said:

I often see this on cars, where the under engine tray is not secured, its like flying a kite under the car

Have you checked this?

Yes I have checked this, my under engine tray does rattle about a bit, but I don't think this is the cause. The flapping sound is very specific and will only happen under hard acceleration in the higher gears (4th and 5th) at low revs. If the engine tray was the cause, I'm sure I would hear it at different times.

What happens if you were to drive steady at higher speeds in 5th?

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4 hours ago, jeebowhite said:

What happens if you were to drive steady at higher speeds in 5th?

Car drives fine, no unusual noises at all. The flapping sound stops when I ease off the accelerator.

Have you checked engine mounts?

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No I haven't checked the engine mounts, but it was one possibility that I gave a fleeting thought towards, but again thought that this would more than likely cause the flapping noise at random times, not during the high gear, low revs times I've previously mentioned. I'll have a look at them, see if I notice anything out of place. Just out of interest, do you know what I should be looking out for if engine mounts were suspect?

When you check them, they would be loose, spongey, disintegrating or missing lol

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Quick update for you.

Just changed the alternator belt, going for a drive a bit later, so I'll see if it makes a difference. However, I don't think the flapping sound is from the belt.

On 8/26/2016 at 6:08 PM, jeebowhite said:

When you check them, they would be loose, spongey, disintegrating or missing lol

I only had a look at the drivers side engine mount, the one that is easily visible in the engine bay, and the rubber felt very spongey, I could push my finger into it quite easily and there was a lot of give in it. I'm presuming the rubber shouldn't be this squidgy?

Nope, they should be firm and not disintegrating

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It's a fluid filled mount, that part actually is squidgy.  Unless yours is leaking the black oily fluid out of the top it's probably fine.  

I must admit, I hadn't read the exact moment that yours happens when skim reading, mine only ever does it under acceleration as well but it can be any gear and revs.  Very weird!

Ok, so one of you says no it shouldn't be spongey, and another says it should be spongey, I'm totally confused now!  Although a bit more research has led me to believe that Tom is correct and that these mounts are what as known as 'Hydro Bearing' type. There is definitely no fluid leakage anywhere around the mount.

My focus likes to make the flapping sound in 4th and 5th gears only, and only at low revs when accelerating hard, and it is a noticeable noise, quite loud. I don't notice the noise in any other gear. It is very strange indeed!

I own the same car as you, James doesn't.  

He is right that on older cars, they used a solid rubber mount which should feel solid.  On a lot of modern ones, our Focii included they use the hydro mount at the top, mine was leaking a couple of months back and had to be changed, I did post pictures of it on here somewhere but I know what the search is like lol.

Oh, and the noise definitely comes from the right hand side engine bay, and only when driving along, revving the car while stationary doesn't cause the flapping sound. Just a thought, could it be Turbo related? As I said it only happens at low revs when putting my foot hard down on accelerator.

2 hours ago, TomsFocus said:

On a lot of modern ones, our Focii included they use the hydro mount at the top, mine was leaking a couple of months back and had to be changed

That explains it then Tom. Did the mount change stop the flapping sound, or are you still getting it?

No the mount didn't change the noise at all.

I have wondered if it's something to do with the vnt vanes, as they're not easily testable like the turbine/impellor wheels.  Bit that really is only a guess, I haven't heard it on previous cars with vnt turbos.