Loud Howling Noise from Front End – Identified and Solved

This is long but (hopefully) worthwhile:

For the last five months, I’ve been struggling to identify a loud howling noise I’ve been hearing while traveling between 45-55 MPH. Since I’ve finally solved the problem, I figured I’d share my diagnostics approach (using a sound recorder) and solution in case others have been struggling with the same or similar issue.

First, the problem:
I’ve been hearing a loud howling noise that sounded a lot like wind noise coming from (what I thought) was the front.

Other facts:
- The noise occurred periodically but only at speeds between 45-55 MPH
- The noise never occurred when it was very humid outside
- The noise occurred mainly while cruising straight
- Vehicle is a stock ’94 SE 2-door 4.0L 4WD 5-SPD with 140k miles

Initial Diagnostic Steps:
- I ruled out wind noise as I hadn’t added or changed anything before the noise started. I further checked the front cowl, lights, etc. for missing screws or other looseness/air gaps.
- I ruled the engine out as the source as the noise continued when I applied the clutch
- I ruled the brakes out as the noise continued when I lightly applied the brakes or lightly pulled the emergency brake
- All the suspension bits were tight with no play
- Ran the Jeep at 45-55 MPH on jack stands (I know, I’m probably a Darwin Award nominee now but I was determined to solve this) but could not re-create the noise
- I was never able to duplicate this noise in the driveway

Poor Conclusion:
- I was so sure at this point that a front hub was the culprit that I replaced them with new Timken hubs and replaced the front u-joints while I was in there. The noise continued (refer to Lessons Learned about replacing good parts ...wasted money and time).
- After reading other posts and sources, I suspected the carrier bearings but I was determined, at this point, to not replace unnecessary parts.

Bright Idea:
- To further diagnose the problem, I purchased a small personal sound recorder from Radio Shack and a couple of cheap microphones. The microphone that worked best was the suction cup kind that attaches to telephones to tape phone conversations. I taped the microphone to the front carrier and went for a ride. I obtained a few other sound samples from various points over the following week (e.g. transmission, transfer case and rear differential) to narrow the noise down. This narrowed the noise to the front-end and also helped eliminate the front differential (and carrier bearings) as the source of the noise.
- After thinking about where this type of noise could come from given the facts I’ve obtained so far, I started to suspect the steering damper. After attaching the microphone to the damper and going for a ride, voila! The noise came in loud and clear!
- I sprayed some WD40 into the damper and the noise disappeared. It must have been reverberating just at certain speeds.

Resolution:
- I replace the steering damper and the noise is gone

Lessons Learned:
- Never replace good parts chasing a problem. I thought I learned that lesson 30 years ago, but I seem to forget every now and then.
- Do obtain as many diagnostic “facts” as possible
- Apply logic to the situation as it always applies to mechanical problems (although some seem to defy logic)
- Don’t jump to conclusions

Thanks for the tip on using a digital recorder to track down hard to find noises. That's a keeper.

You could also analyze the noise by slowing it down once you have it recorded.