Last summer I bought a used 2013 BMW 528i xDrive with 65k miles on it. The dealer had to put on new brakes and a new transfer case, but since then it’s been running really well. However, a few weeks ago I noticed a really strange occurrence: when the car is in park I hear and feel a quiet tap once every 2-3 seconds. I hear it through the floor board and it seems to be coming from the engine compartment. It’s does not seem to increase in frequency when I rev the engine, though it’s quiet enough that even just putting the car in drive makes it barely audible. Opening the hood and trying to find it there seems all but impossible as the noise is not really audible. It’s much more of a “feel” than “hear” thing.
I am wondering if this is the sound of impending doom. How can I prevent my and my car’s early demise?