Tracking down a noise in a 2004 Jeep Wrangler

Maintenance/Repairs
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1

I’m stumped. 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’s 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.

Another possibly helpful clue: 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.

Any ideas?

2

4WD or AWD? Could be a CV joint, possibly an inner joint making the sound. Could also be in the front differential.

3

Worn transmision gear synchronizers. The snow on the road absorbed some if the sound instead of reflecting back into the cabin.

4

Since I have a knocking type sound that appears only when I have my tranny in D and I’m stopped, and I know for certain what’s causing it, allow me to suggest that yours might be from the same source; plastic parts; splash shields, wheel well liners, that sort of thing. I fixed mine, but now that the weather has grown cold the sound has returned. I have to get the car back up on ramps and go at it again. There’s so many plastic parts with cheap plastic fasteners holding them together that it’s amazing there isn’t more of the sound.

5

@same
Yours is definitely a first look and see before going and further. Didn’t think of it.

6

I just went through a similar mystery, only on starting, my mechanic, cause it has been freezing cold, did a few false tries, but ended up a new serpentine belt as it was worn, after 150k, ok, and two new idler pulleys, one was walking and the other was ticking only when cold, but could be something to look at. Here was it at it’s worst, http://www.youtube.com/watch?feature=player_embedded&v=MN3thuj80Ow

7

I think you have a cracked exhaust manifold. You might be listening to the tic, tic, tic of the exhaust pulses of one or two cylinders. This is usually louder when the engine and manifold are cold.

With the engine cold open the hood, start the engine, lean over close to the exhaust manifold and snap the throttle open from idle to 1500 RPMs a few times. If the manifold is cracked/leaking you should be able to hear the leak.

8

That kind of ticking in Jeeps is usually a worn U-joint. I’d check all the U-joints in the front driveline (may as well inspect the rear driveline while you’re at it) and I’ll bet that one or more of them are a little loose, as in you can wiggle the joint from side-to-side in one or more directions.