There's a squeak from the clutch when pressing/releasing it but only if:

1) The car is warm
OR
2) The clutch was used for a long time (more than 15 minutes on city traffic)

I haven't been able to determine if 1 or 2.
I should leave the car on for 15 minutes and check if there is the squeak without pressing the clutch at all.

Most strange to me is that after a few hours, when the car is already cold again, the clutch works again without the squeak, as if the existing problem had been solved.

I changed the brake fluid some time ago, but I didn't flush brake fluid at the clutch. Could this affect? I'm not sure if the squeak started after the brake fluid change.

Few weeks ago I left the car in the indy shop and they lubricated "something" on the clutch system, but the squeal continues in the same way.

 

Can't hurt to have someone who knows these cars check it out, but it could just be the typically noisy dual mass flywheel we have on these. If you're running the stock clutch, it could just be that and it happens intermittently. If you've replaced the clutch with something that's not a dual mass flywheel, I'd be more concerned.

Are you getting any clutch slippage when shifting gears?

 

NJ Mini,

the clutch was replaced last November in an indy shop (clutch slippage) and all was working without noises during 2 months.
Before the clutch change and during the clutch slippage period, there was not clutch noise at all.
It seems is related with the temperature, because when weather is colder, the noise is less often.
Strange for my almost null knowledge