So I'm trying to help my neighbor.
He's got I think an 05 I think. He was unsure of mileage but I can find out.

He just replaced oil pan gasket, crank position sensor o-ring, tensioner, and I think he said passenger axel.

He's got this loud sound coming from left horn. He said the rubber boot on the side of the intercooler had oil in it.

No mods for extra SC noise.
It's just.. suddenly real loud on left horn area. Anyone know what it could be?
Thanks.

 

This is only a guess based on what I have read here and elsewhere, I hope this is not it but I have read that when the SC starts to go, noise is the first symptom. I think a little oil in the intercooler boot is normal. Have you checked out the water pump? It is on that end of the SC(left, when sitting in driver seat, correct?) Any issues with coolant leak or overheating(just thinking out loud here)When the water pump start to go it will leak/weep coolant. There are some great videos on YouTube for removing and servicing the SC and water pump: Here's hoping it is NOT the SC. Good luck and Motor on!

 

Left when standing infront of the car.
So passenger side horn is where the noise is.
Sorry for not stating that.

No coolant leaking and no issues with over heating.

Oh and tensioner has been replaced. Noise still persists.

Right? Neighbor is hoping it's really not that. He's replaced so many things in the past 6 months that he's over it. lol.

 

Ok, so I had a similar problem a couple years ago. I drove to work no problem, I got in car to drive home, loud noise, very loud and very worrying. I drove it straight to Mini as I had not found an independent near me. It cost me a diagnostic($120) but it turned out it was my alternator. I had never heard anything like that and could not pinpoint the racket myself other than, "it seems to be coming from over here(waving of hand)". Not sure how they figured it out but I swapped it out and have not had a problem since.
I am no mechanic but maybe if you were to hold something like a screwdriver or metal rod against the alternator while the car is running you would be able to feel any noise or vibration?
My car had I am going to guess around 90k miles on it at the time and it happened all of a sudden.
Good luck!