Signs and symptoms of a motor going bad
I have a 99 Civic Si with 180K miles. Last winter I started hearing a noise coming from my motor that sounded like a zipper. It would speed up/slow down with the engine RPMs, didn't matter if the clutch was engaged or dis-engaged. I thought it was something with the timing belt, so I had that replaced last summer (it was due for it anyway), and also had the mechanic check out the engine at the same time. He said the engine was solid, compression was good. He thought it needed a valve adjustment (probably because of the noise), but found that it was within normal ranges and did very little adjustment, but the noise was still there.
Yesterday morning, I noticed that the sound was significantly more noticable, to the point of annoying. It now sounds like a cross between an alternator whine and supercharger whistle. I don't have a supercharger and the alternator was replaced a couple years ago, before I had the car. The noise also does not get worse or fade out when electronics are turned on and off. It starts getting noticable at about 2500 RPMs, and gets worse from there. It was the same today, and sound exactly the same after the car is warmed up.
I don't drive the car hard, and I keep up with maintenance on it.
Any idea what could be happening here?