Chirping sound out of engine.
 

I have a 1999 Boxter 2.6L that emits a chirping sound when it idols. With RPM's it gets quieter, but is barely audible. As it warms up, it gets noisier. Have opened engine access, and is not a pulley or belt. Any ideas?

Rik

Get the chirping sound going at idle.
Use a section of hose like garden hose or the like.
Use it like a stethoscope.
Locate what side or end of the engine it is coming from.
Work from there.
You should be able to locate the sound with a little effort.
Sometimes a loose spark plug can cause what your describing.

A loose spark plug will cause that.

I've got something similar, tried using PVC pipe to locate what I had suspected was an idler pulley. No luck. How does a loose spark plug cause that chirping sound? I'll give a listen to the plugs, but I'm just curious how it would make the sound.
-Thanks for the advice.

Escaping compression makes the noise.

Replaced the spark plugs. The old ones weren't too bad looking, and looked relatively uniform, but didn't fix the chirp. I'm tempted to put a dab of penetrating oil on the bearing of each idler pulley one at a time to see if that temporary stops it and therefore identifies the culprit.

Someone correct me if I'm wrong (someone usually does!), but I think you can safely accomplish the same thing by taking off the belt (easy) and running it briefly to see if the sound is gone.

Let me know if you figure it out---mine's been making what I think is the same sound for a while now. I've thought it's pretty innocuous sounding, and isn't getting worse, so I've been ignoring it.

Had chirping sound...didn't figure it out until the water pump pulley fell off.

+1 for great first step. If noise is gone with belt off, you just have to identify the offending pulley.

My chirp starts when I start the engine, but then goes away almost immediately (at idle). It gets louder at higher RPMs and when the engine is under load. I'll try the recommendation to briefly run the engine without the belt.