I had a co-worker start and stop the engine while I listened to for the noise. It appears to be loudest near the intake manifold/fuel injectors.

The squeak/squawk is louder if the engine is warm. In addition to the squeak, I also hear "sizzling" (kind of like water on a hot pan) type of sound near the injectors as well as the hissing sound of something de-pressurizing.

Any ideas?