Evening, all. Tonight, my car decided to start making a new and annoying noise. I was hoping you guys could help me figure out what it is.
There is a “pit-pat” sound coming from the engine bay, and to my untrained ear it sounds as though it’s coming from the engine itself. It’s only detectable at idle and low RPM - over 1700 or so, the frequency is too high to pick it out as a unique sound and the engine roar overwhelms it.
A friend of mine and I looked at it tonight. We first thought that the oil was low, but a quick check showed ample levels. Our next hypothesis was that one of the valves needs adjusting, but I won’t be able to confirm that until I take it in.
Here’s a link to a recording of the engine idling. It’s from my iPhone so it’s not exactly the highest-quality sound clip in the world, but you can very clearly hear the pit-pat sound I’m talking about:
If it matters, the car in question is a BMW Z3 2.3 Roadster, model year is 2000, it’s got about 31,500 miles on it and just had its Inspection II done (and passed with flying colors) at 30,000.
If there’s any additional information I can provide, let me know and I’m on it. Thanks guys!
I’m guessing, but the sound and the fact that it gets less noticeable at higher RPM mahes me think that it’s some sort of valvetrain noise. I think that your engine has a fairly complex setup to drive the camshafts–multiple timing chains, double VANOS (I think), etc…
Of course, I have no idea of what is specifically wrong or how much it will cost.
Beats the hell out of me.
The fidelity is not such that I can’t call it one way or another.
It could be valve train, it could be a bearing in a belt pulley / idler.
I just can’t tell from that recording.
The mileage is so low it’s hard to suspect something major. However, the age factor still comes into play. The noise may be just a stuck valve lifter. But it sounds lower pitched than that. Your first guess of low oil may have been correct. It sounds almost like a slight rod knock. The frequency is more like that then valve train noise. Perhaps your oil pump or the oil pump relief valve has failed.
Thanks, all, for the replies. I just got an appointment with a mechanic for tomorrow morning, so hopefully we’ll get a definitive answer then.
I went out to check it again this morning after letting it cool down through the night. The oil level is okay (side note: BMW dipsticks are ridiculous - mine’s like a rocket ship on a kebob), and it looks clean. I also turned it on and put my hand behind the exhaust - perfectly even. A random website told me that if it was uneven or “pulsing” then that would indicate a valve issue, but who knows. Mostly it just made my hand smell.
