Mine 2013 X1 sDrive28i just hit 115k miles. Had the A/C compressor replaced under warranty and nothing else. Last month the engine started to make a very loud whistle noise. Changed the drive belt, tensioner and pulley. didn't work. After that my Indy mechaninc opened the valve cover to inspect the engine and had no luck to find the origin of the noise. Total cost of USD800 for labor and parts replaced and the noise continued. Indy mechaninc suggested me to replace the engine, he told me that could be timing chain but he didnt have the right tool to do the job (!). After some search on internet I found out that the origin of noise was the PCV valve diaphragm that was ripped apart. Replaced the diaphragm by myself in 5 minutes for a total cost of USD30......
