I have a noise coming from the engine bay area. It sounds like belt noise or bearing whine (although it is a slightly lower pitch than an accessory belt slipping).

It has been there since I installed the 2L a couple of years ago, is intermittent, occurs between idle and 1800rpm and I just can not nail what is causing it. It is driving me mad, every time it occurs and I get out of the car to investigate it goes before I can find it. Over the last 2 years I have done the following,
1. Swapped out accessory belts and re-tensioned.
2. Replaced clutch, flywheel and associated bearings.
3. Replaced Cambelt, associated bearings and re-tensioned.
4. Removed the GM coolant sensor from my cylinder head exit pipe (in-case flow around it was causing cavitation and noise somehow).
5. Removed my Mk1 CAS from the back of the exhaust cam (again in-case it was causing a noise).

The last 2 were done due to the fact that it seems louder near the passenger footwell (exhaust side).

The only items that remain that, I can remotely imagine, could cause a noise such as this is the turbo bearings (no sign of failure or reason to suspect) or the FM adjustable cam gears??? Both were new with the install. The new (Gates Racing) cambelt walks a little on the cam gears - back and forth about 1 to 2mm. Could it be the belt driving the cam gears causing the noise? Bad idea to lubricate the cam gear teeth with silicone spray to see if it goes? Likely to allow the cambelt to slip a teeth?

Anyone else had this sort of noise? It is actually quite loud in to cockpit when it is occurring (although is more difficult to hear outside the car due to engine/exhaust noise) and is just driving me crackers!

 

Perhaps the infamous clutch rod squeak?

 

You mean when depressing or releasing the clutch? I greased the mushroom bolt end when installing the new clutch and flywheel and having the clutch up or down makes no difference when the noise is manifesting itself -so I'm pretty sure it isn't that. If I understand you right.

I know an engine bay noise seems pretty trivial but it is driving me crazy and trying to eliminate it has become an obsession now.

 

I only mention this because my Fathers car had this only 2 weeks ago. While he was away in the Isle of Scilly he left his car in Newquay. When he got back it wouldnt start, so rang Greenflag who said its probably the battery as it was reading low. Charger and 15mins later they crank the engine, normal starting noises but no actual start. "Give it a longer try" is uttered, after 15-20 seconds of trying there is plumes of white smoke coming from the bay. The alternator shaft had ceased onto the casing and cranking the engine was producing the smoke. Anyway a tow home 4 hours away and a new alternator fixed it. Might be worth swapping out to check. Apparently its a bread and butter service for airport garages