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Have a 2011 Mini Countryman, R60S turbo engine. Had the classic oil filter/cooler housing leaks, both gasket sets replaced as well as a cracked intake housing. It has a slight knock/tap type of sound that I would describe as a loud fuel injector. Strange thing is it goes away above 1,500RPM. No performance or drivability issues. (There was no coolant in the oil or oil in coolant.)
'Dad's Automotive' could not get the oil leak issue fixed in a timely manner since it involves pulling the front end of the car off to gain access (and I am limited to my 'driveway workshop'). Anyhow, took it to a very competent shop which has 40 years experience working on imports, about 100 miles away (everywhere is 100 miles away form here). They did a great job and were quite puzzled by this knock/tap sound and if we had not been already there and from so far away the shop owner would have liked to look into it more because he was puzzled.
As mentioned the noise goes away above 1,500 RPM. It does not seem to be related to load. They did a cylinder contribution test thinking that lack of combustion pressure in a cylinder would change the noise, it did not the noise was the same. It seemed to them the noise was coming from the cylinder 1 end the engine. They even called and asked me to email them any codes I had scanned and saved, which I did, but the only DTCs were camshaft position errors which I guessed were due to low oil pressure (freeze frame data seemed to indicate it was a cold driveaway condition.) With the oil leak fixed there is no further camshaft position codes.
My fear was that the leak was sudden and severe enough that the engine was starved for oil and there was bearing damage. It does not sound like a rod knock, etc. and they found no evidence/shavings in the engine oil. They did mention that the timing chain tensioners are known problem areas but it was odd that the problem was only at low RPMs and there was no noise when decelerating from highway speeds (reduction is load) when you might expect a loose chain issue.)
In my research, I only found one report of a chain tensioner causing a similar low RPM noise. I did find a curious post saying that on a GDI engine that low fuel pressure at low RPMs can cause very loud injectors and as the RPM/fuel pressure increases the noise goes away. I have not heard of this before and can only guess that the low fuel pressure is providing less force to push against the spring that closes the injector which lets it close more forcefully creating the noise.
So, I'm guessing the next step would be to check the high pressure fuel rail sensor PID and see how much variation in pressure there is from idle to 2,000 RPM. When the shop did the cylinder contribution test I'm not sure if they did so by cutting fuel or spark to each cylinder so perhaps unplugging injector 1 and 2 (one at a time) would reveal if it is indeed a noisy injector.
I'm just thinking out loud here hoping that someone might have some pointers. I'm guessing the timing chain tensioner might be a good thing to replace as a preventative maintenance issue ( I hear BMW is on the rev 5 of this part now).
Did some more 'desktop diagnostics' and her Mini sounds like this: . Will start with the simple stuff before delving into jumping into more complicated stuff.
