I recently purchased a 2012 825i at auction. The machine has 2900 hours. The engine is running rough and has a knock (or a tick, not sure I know the difference). I am going to list what I have done to diagnose the problem and I am looking for suggestions on what else to do before pulling the motor and opening it up. I started off by changing all the fluids. No noticable shavings in the oil. I also drained and replaced the gasoline. I have pressure tested the fuel pump, which is a little below spec (40 psi). I have tested resistance on all the coils. The resistance is the same for all, although I can't find a spec to compare it to. I replaced the spark plugs. I have done a compression test on all three cylinders. They are all at 100 psi, give or take a few. I believe this is a low, but that could also be my compression tester. I have checked the timing belt. It is in time and the belt looks to be in good shape. I also did a leak down test on the cylinders and only had small amounts of air escaping (well within tolerance) from the dipstick tube. I have never worked on a DOHC motor before, but I have rebuilt other types of motors. I have a copy of the service manual. Any suggestions on testing before I dig into it?