For the past year, we have been hearing a strange "pinging" sort of noise at seemingly random times on a 2011 Outback that we bought used with 110k miles in 2024. (I say pinging because, to me, it sounds reminiscent of the engine ping I remember as a kid driving my parents' Chevy Caprice.) We made a recording, which turned out better than I expected:
What I'm trying to describe is the very high-pitched, almost metallic, repetitive sound at perhaps 10 Hz repetition rate. It comes and goes over the background road noise.
We are still going to try a tank of 93 octane fuel to see how that affects it, but diagnosis is tricky. We have gone hundreds of miles without hearing the sound at all, then it seems really severe, then we try to have a mechanic listen, and of course it goes away. When it's really going strong, it is quite alarming... not at all subtle.
The noise does seem to happen more often after a long day of driving on a road trip. We don't normally hear it at highway speeds (possibly too faint?), more often in 2nd, 3rd, and 4th gears as we slow down for a speed zone. It mostly seems to happen in the mid-2000 RPM range. It may be more frequent in hot weather, yet it has happened in 50s/60s F weather also. It has also been quite severe crossing a mountain pass at 8000'+ elevation, which seems unlikely if it is really engine ping? At this point, I'm split 50/50 on engine vs other mechanical source.
Maybe if I analyze the recording enough, I could isolate the "pings" and find the exact repetition rate. By my calculation, at 2400 RPM each cylinder should be firing at ~ 20 Hz, and I would estimate our ping repetition as closer to 10 Hz, so does that point toward a non-engine noise source?
It is definitely not tied to wheel RPMs.
What I'm trying to describe is the very high-pitched, almost metallic, repetitive sound at perhaps 10 Hz repetition rate. It comes and goes over the background road noise.
We are still going to try a tank of 93 octane fuel to see how that affects it, but diagnosis is tricky. We have gone hundreds of miles without hearing the sound at all, then it seems really severe, then we try to have a mechanic listen, and of course it goes away. When it's really going strong, it is quite alarming... not at all subtle.
The noise does seem to happen more often after a long day of driving on a road trip. We don't normally hear it at highway speeds (possibly too faint?), more often in 2nd, 3rd, and 4th gears as we slow down for a speed zone. It mostly seems to happen in the mid-2000 RPM range. It may be more frequent in hot weather, yet it has happened in 50s/60s F weather also. It has also been quite severe crossing a mountain pass at 8000'+ elevation, which seems unlikely if it is really engine ping? At this point, I'm split 50/50 on engine vs other mechanical source.
Maybe if I analyze the recording enough, I could isolate the "pings" and find the exact repetition rate. By my calculation, at 2400 RPM each cylinder should be firing at ~ 20 Hz, and I would estimate our ping repetition as closer to 10 Hz, so does that point toward a non-engine noise source?
It is definitely not tied to wheel RPMs.
