I'm always paranoid about any strange noises my MINI makes, but in the last day or so have noticed a new one.

I've just been out for a few runs up and down the bypass at naughty speeds to try and pin it down a bit more.

It's a kind of chattering squeak, a bit like a turbo wastegate noise, and seems to occur under acceleration between 4000 and 5000 rpm. My initial fear was that the clutch was failing, but the conditions under which it occurs seem a bit specific for that, and the clutch feels fine.

Anyone got any ideas? He's going into Chandlers for his MOT tomorrow so I shall ask then, but since it's unlikely to be something which can be diagnosed by plugging it into a computer, I'm not expecting much luck.

You could ask TWG!

The guys are very helpful

Neil I had a similar noise on my old R53 it only done the same similar noise when it was under hard acceleration between 3000rpm and 4000rpm coming from drivers side behind front wheel it was kind of a metallic clicking sound. on normal acceleration it didn't do it.
Turned out to be the harmonic balancer in other words the bottom pulley wheel on the end of the crankshaft which runs the belts.
my car had its original one on and BMW made a modified one so I had a second hand one fitted and bingo stopped straight away. The old one has a larger piece of rubber and it splits over time the modified has less rubber.

Hope this helps. 

Well the squeaks from the engine bay have got more persistent - he now does it on startup for a few minutes until warmed up.
 
Suspect it's going to be a pulley or belt replacement needed, so he's booked into Chandlers for them to take a look next week.

That will be intresting I still think its bottom pulley

I think that's likely, now he's doing it while I can get out and listen, the noise is definitely coming from the area you mentioned  

What was the cause? We have seen and replaced a few bottom pulleys (like Gazza says) and few alternators for similar noises.

Hoping they're going to find out on Wednesday  

I shall be laying on the beach in Benidorm then Neil  

I might be on the beach in Rustington  

Have you had the car fixed yet Neil ?

Drove him to Goodwood and back on both Saturday and Sunday ... no noise.

Tuesday morning, got him out to wash him ... no noise.

So postponed his visit to Chandlers.

Yesterday, driving home from work ... the noise was back   

So if it carries on over the weekend, will take him in next week.

Well he's been in to Chandlers today for the noise to be investigated.

A faulty belt tensioner has been diagnosed, and parts ordered, so hopefully he'll be fixed tomorrow  

That's good news Neil

Fingers crossed Neil - and that he shines at Santa Pod

They couldn't get the parts in to fix him today, so I won't be getting him back until tomorrow.

The good news is, it should mostly be covered by the extended warranty.

Glad it'll be all fixed soon And even better that the warranty will cover it

And he's back ... just been to collect him, the squeaks and chattering have all gone, and the only noises he's making now are the ones he's supposed to  

Only had to pay for a new belt, the warranty covered the rest  

That's good news Neil, bet you're glad to have him back whining and nothing else again

Awesome news Neil!

Whining and popping and nothing unwanted   

Been out in him tonight, it's great to have him back to his true self