Disco 2 Whistling Discovery?

This is just about driving me crazy. At 50mph or thereabouts an annoying whistle starts (800Hz), very audible in the cab. It has just started, after doing nothing on the car and is NOT effected by any of the following:
1. Heater controls.
2. Sun roofs
3. Windows
4. Wipers.
5. Wing mirrors
Now, the car does sit below a tree and leaves do fall on the vehicle, however the car can be perfectly clear of leaves (blown out). But my feeling is that this is a leaf stuck in the heater intake before any of the control system but I cannot see where the heater intake under the bonnet is to check.
Whilst it is difficult to pin point to location of the whistle whilst driving my partner seems to think it is in the center area of the dash.
I thought it may be an old parking ticket that has worked its way down the screen demister vent, but blasting the screen demister does not dislodge anything and makes no difference to the damn whistle.
Any ides before I torch the damn thing?

Turbo hose might have a hole or split or hose clamp not tight.

warped exhaust manifold or blowing turbo gasket

Thank you for the ideas guys, but this only happens when the car is moving at above 50mph regardless of revs. It is not replicatable at rest or just revving the engine. Therefore I am assuming it is air pressure on the front of the car.
Can anyone advise where the air enters the heater/ac system. Looking at the back of the bonnet the air just seems fed into the engine compartment. Am I missing something?

Stevehh said:

Thank you for the ideas guys, but this only happens when the car is moving at above 50mph regardless of revs. It is not replicatable at rest or just revving the engine. Therefore I am assuming it is air pressure on the front of the car.
Can anyone advise where the air enters the heater/ac system. Looking at the back of the bonnet the air just seems fed into the engine compartment. Am I missing something?

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mine whistles similarly not when stood but under load ie accelerating not when coasting

Does it do it when you switch of the heating (fan) as well? Mine was also whistling and for me it was the bearing of the blower motor.
(this is not speed dependent, but you can check, maybe)

Blimey that knackered.....

The whistle in my S2 is NOT effected by any of the following:
1. Heater controls.
2. Sun roofs
3. Windows
4. Wipers.
5. Wing mirrors

So, has anyone any idea what the path is to get air into the heater system. As I mentioned before it looks like the air inlet vent, behind the bonnet edge, just enters into the engine compartment. Where is the air entry into the heater/ac system?

The air inlet for the heating/cooling is under the hood just under the windscreen (long opening covered with foam normally). Is it what you are looking for? I do not think that it can couse such noise. Have you checked for example hand brake asm? The other source of vibration for me was the hand brake drum (for me it was from 2700rpm).

Thank you Berg.
Interesting, the bonnet forms a cavity at the rear when it closes against rubber seals. Air is fed into this cavity from the outside below the windscreen, through the foam rubber "Pollen filter" and there are entries into the vehicle heater/ac unit both on the passenger and driver side at the rear of this cavity on the bulkhead. The passenger entry is fairly easy to get you hand down and see if there is anything blocking it, the driver side less so. Access is really bonnet off, windscreen side trims removal and then the facia at the lower windscreen, where the wipers come through. Quite a faffy job especially regarding the side piece clip arrangements.
Anyway nothing found there.

I like the idea of the handbrake drum assembly causing the whistle, that is possible as it is road speed dependent and could be proven by applying the handbrake whilst in motion.

Thinking about it, this whistle started after I removed the passenger side wiper to wrap PTFE tape around the spindle to overcome yet another aftermarket failed arm spline. They are really crap.

Just one more interesting thing.. My wife's Honda has a side window deflector which exactly creates similar noise what you have described. If I slightly lower the window (few mm) then the whistle goes.....

Taking the scuttle off is easy, bonnet bolts off. Shut bonnet and slide forward 12 inches. Wipers off via small hidden nut, panel off via larger nuts on spindle.

You may have a hole in the edges of the vent. Seal with Sikaflex. You can check for rust (i know really!) while your at it

Once had a whistle like this. Turned out to be a leak at the top of the windscreen, but on a D1.

jamesmartin said:

warped exhaust manifold or blowing turbo gasket

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Just done my exhaust manifold bit of a pig , broke a easy out in one of the studs that had broken, I had 3 broken studs I ended up re-taping them, cut the broken easy out with a dremel, used to make more noise when engine working hard

Ian M in France said:

Just done my exhaust manifold bit of a pig , broke a easy out in one of the studs that had broken, I had 3 broken studs I ended up re-taping them, cut the broken easy out with a dremel, used to make more noise when engine working hard

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As some of you know, I had the same problem but was "lucky" enough not to break an "Eezyout" (What an oxymoron that is).
They charged me double to skim it as it had warped so far!!
The whistle sounded like a drivebelt, so I kinda ignored it for about a week, not that that woulda made much difference!!
What did they charge here in Frogichops land to machine the manifold? Just for comparison with UK prices?

Stanleysteamer said:

As some of you know, I had the same problem but was "lucky" enough not to break an "Eezyout" (What an oxymoron that is).
They charged me double to skim it as it had warped so far!!
The whistle sounded like a drivebelt, so I kinda ignored it for about a week, not that that woulda made much difference!!
What did they charge here in Frogichops land to machine the manifold? Just for comparison with UK prices?

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I had a spare one off of another engine, all looked okay so fitted that and seems okay,

Ian M in France said:

I had a spare one off of another engine, all looked okay so fitted that and seems okay,

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Did you cut between the webbings to ensure it didn't happen again?
Hope this doesn't mean you tearing your hair out!!

Stanleysteamer said:

Did you cut between the webbings to ensure it didn't happen again?
Hope this doesn't mean you tearing your hair out!!

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No ****, Might have to take it off again and do that

Ian M in France said:

No ****, Might have to take it off again and do that

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Oops!
Well at least the nuts and bolts should come undone relatively easily!
Better earlier than having to go through the whole nightmare again in years to come.

Well thanks for all your input on this irritating problem and I am pleased to report I have solved it (sort of). I decided to bring the leaf blower and compressor hose into action with a mate installed in the cab to listen and see if I could replicate the whistle whilst the vehicle was stationary. Needless to say I couldn't, but blasting high pressure air into the heater intake under the bonnet cleared the problem, even if I am still unsure exactly the cause. My guess was as I first thought, that a piece of detritus had lodged somewhere in the passage to the heater mechanism and was vibrating. Anyway we are now whistle free and the LR is no longer under threat of torching.