I had a 146ti that I sold 2 years ago.
The car developed a serious problem at around 15,000 miles.
The car had a problem with tappet noise. The engine sound was perfect from cold, and was fine when warm/hot, but if you started the engine from warm/hot it would sound like a tractor.
The main dealers had quite a few attempts to sort the problem.
They tried mobil 1 oil, but this did not improve the sound. They then replaced all the hydraulic tappets but this did not cure the problem.
Finally the cylinder head complete with cams and tappets was replaced, this completely cured the noise.
All this took 6 months to be resolved.
The car had never run low on oil.
The only conclusion the dealer could come up with was that the bores in the cylinder head where the tappets sit had worn badly and that the oil when warm/hot was running past the tappets.
I heard from the warranty guy at the time that there was another car in the area with exactly the same problem.
Previously, 146TI, 147 2L, Brera 2.2, Mito 135MA