Jeep - Wrangler :: 2004 - Metallic Tapping Or Ratcheting Noise

I've got a 2004 Jeep Wrangler SE 5-speed with 83,000 miles on the 2.4l PowerTech engine in it, and it's making a very strange noise that I can't pinpoint.

So first, the noise itself. It sounds like a metallic tapping or ratcheting, like the sound of raising of a large chain hoist. Fairly high-pitched, audible inside and out. Not incredibly loud (I have to point it out to passengers) but loud enough to bother the hell out of me. The closest I can come with location is "somewhere under the hood."

However, the noise is only present under certain conditions:1. The transmission must be in gear. Forward or reverse doesn't matter. Revving engine at idle does not produce the noise.2. The transmission must be under load, i.e. when accelerating or releasing the clutch in 1st to begin driving. Letting off the gas stops the noise.3. The noise only exists somewhere between 1k and 2.5k rpms. Application of throttle at any road speed in any gear with the engine in that RPM range produces the noise. 4. The frequency of the tapping increases with engine speed. 5. Ambient temperature appears to have no effect, but as engine temperature increases the noise tends to disappear. Not always, though, as it shows up sometimes when the engine is completely up to operating temperature. 6. I don't notice any kind of performance issues related to the noise. Power's normal (for a 2.4l Chrysler 4-banger, that is) and gas mileage is within the EPA estimates.

Things I've investigated:1. I'm pretty sure it's not lifter noise. A bottle of Seafoam made it run better, but the noise persists. 2. I've checked the catalytic converter heat shield. It's on tight. I found the flange where the exhaust manifold meets the downpipe was a bit loose, but tightening it down didn't eliminate the noise. Getting underneath and shaking the hell out of every component of the exhaust system I can reach produces no results.3. Engine mounts show normal wear. Transmission mount appears fine. 4. No check engine light, and all gauges read normal. Hooked up a code reader for fun and it came back with nothing.

As the noise only shows up while driving, I can't just crawl under there and poke around. The best I can do while driving is feel for related vibration, which gives me nothing. Whatever causing it, it's not transferring up through the stick.

In the may-or-may-not-be-related category, I've got a bit of oil consumption and a clunky transmission, but according to the various Jeep forums I've found, those seem to be fairly normal.

We got some snow the other day, and as I cleared it off I allowed the car to warm up for about 20 minutes. When I got in and drove it, the noise was greatly reduced. Not gone, but barely perceptible.

I spent a couple hours on YouTube the other day, trying to compare my noise to videos of other Jeeps with drivetrain issues, and found nothing even close to similar. Whatever's making this noise, it's not common.