Help me diagnose strange noise

[Kozzy]

To keep things simple I will list the symptoms of the noise:

- Noise best described as a ticking noise, very similar to engine knock but slightly 'softer'
- Noise starts at around 15 MPH and is not audible below this
- It does not change pitch, volume or frequency. Once the noise starts it stays exactly the same
- The noise is the same despite engine speed or road speed, whether or not in gear, with or without brakes on
- Noise does not change going up or downhill or over bumps etc or with varying degrees of steering lock
- Can only really hear the noise with the window down and can hear the noise 'reflected' off parked cars etc as I pass them
- Nothing has changed with the car in around 6 months and the car is always run on Shell VPower, the noise has lasted over 2 tanks of fuel

This is a very odd noise and I have only noticed it over the last week or so (may have started sooner but only recently started driving with the windows down again).
Because of the constant nature of the noise I had wondered if it could be something electrical, alternator for example?

The car: '98 version 4 STi Type R

(also posted on scoobynet)

[Kozzy]

I guess the ticks are around 3-4 a second and constant after the car has got moving. My instinct was something like the alternator but I don't know if it is constant speed. Your idea of removing the drive belt would probably rule this possibility out quite quick so will give that a try in a bit.

While searching around others seem to have had similar symptoms that pointed to a loud boost solenoid. Do the solenoid acts regularly? I would have thought they would change based on throttled position / boost? My noise is very regular.

Edit to add: RBWill, they do seem like possible candidates too now, I can see me pulling all of the drive belts off at this rate :S

Edited by Kozzy on Tuesday 5th February 13:40

[Kozzy]

Well I've had a bit of a look under the bonnet and I am almost 100% sure it's not the boost solenoid, it is clicking away quite quietly. The noise appears to be coming from the right of the engine somewhere beneath the alternator (again alternator seems to be making no noise). Could this be a bearing in the water pump?

I will have a proper look under the bonnet over the weekend and maybe even record a short vid to see if that can help shed some light.

[Kozzy]

I took the car out last weekend and drove it along a quiet road where I turned the engine off and coasted from 30 to almost stationary. The noise continued long after the engine had come to a complete stop and didn't change when in/out of gear of clutch depressed or not. I am leaning more towards something actually rattling now.

I got my other half to film a (rather boring) vid of the dash so the noise could be heard and will post this up if I can't get any further.

What heat shields (and where are they located?) are likely candidates?

Cheers for the input guys, much appreciated.

Edited by Kozzy on Friday 1st March 16:25