Car making roaring noise

Make: Ford
model: Fiesta MK4
year: 1998
mileage: 70 000
engine: 1300 cc

My Ford Fiesta began making the roaring noise apparently not caused by anything. The noise resembles the sound of the airplane propeller and it is proportional to the speed - at 25kmh (15mph) it begins as the low frequency sound barely heard and at 60kmh (37mph) it's louder then the engine revving; Its not ugly grinding and irregular but exactly proportional to the speed.

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It seems that noise appeared on a 10 minute trip on a rainy day:

- I was driving 5 minutes - everything normal
- I pulled over and the engine overrevved (another problem) and I tried to calm it by depressing the clutch a little (not violently)
- as soon as I begin to drive back the noise appeared and I mistaken it for the engine sound (slipping clutch).

Its louder when sitting in the back seat.
Its not the radiator fan.

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Another unusual things prior to the problem appearing (but after that everything was normal for 3 days):

- forgot to turn of the engine when parking and took the foot of the clutch
- scraped the gear a little once (didn't press the clutch enough)
- sprayed WD40 all over the engine and behind the wheels (in the steering mechanism joints and the suspenders)



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*
* This noise is heard even when gliding with the
* CLUTCH DOWN, GEAR IN NEUTRAL and
* ENGINE OFF.
*
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Thank you,

Hrvoje
:)