I've got a noise coming from the engine of my 2007 Civic EX. The car sounds like a 1980's Mercedes diesel. From what I've experienced in the past, it sounds like a spun rod bearing. Contributing to this is the fact that when I checked the oil when the noise started, it was really low on oil (I'm checking the dipstick a lot more often from now on!).

However, what's throwing me is that the sound isn't present until you rev up to about 2,300 RPM. If you then let off the gas, the sound will stay until it goes beneath about 1,800 RPM. If you keep going up from 2,300, the noise will disappear at about 3,500 RPM and then reappear around 3,800.

I haven't drained the oil yet, but I've pulled oil off the dipstick several times and I can't see any shinny specks of metal. I was thinking maybe the valvetrain, but I refilled the oil and the noise didn't go away like I expect it would if it was a low oil related problem in the head.

Maybe I'm just being hopeful, but is there anything else it could be?

 

If you know you've ran it low on oil and it now has a knock....probably the main/rod bearings

 

Yup, I had a mechanic confirm. It's a spun bearing. Damn.