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?

 

Just had the car at the mechanic. A/C pulley (tensioner) went bad.

 

kinda sounds like a pulley is going bad....did you replace the water pump with the timing belt? could also be the tensioner pulley or one of your accessory pulleys...you could pull off the drivebelts and see if it still makes the noise to eliminate or pinpoint the possibility of your a/c, alt., or p.s. pulleys.

 

i have this exact same problem and the exact car but mione has 53,000 on it

 

Yep, it was one of the A/C pulleys. Not the one on the compressor itself, but there's one just off the compressor.