Hi all, I was recently on the freeway driving on flat roads crusing at 75 when seemingly out of nowhere I heard a loud pop, then an onset of a very loud rattle. The pop sounded like a bolt breaking or something under a lot of tension breaking, and the rattling sounds fast, but not quite drive shaft fast, I approximated 6 or so smacks per second. The odd thing is after letting off the gas and slowing to about 60, the rattle went away and it drove normally.
As a side note, the location of the sound seemed to be behind the driver side dash, or right in front of the firewall on that side, "engine side".
Upon pulling over I looked at the blades on the cooling fan, this is a four-cylinder model, and none of them were loose. This is when I started poking around the engine compartment to try and find things that were loose, the airbox was jiggly so I bungee corded it down and went on the road again for the noise to come back at the 65mph threshold, not the airbox.
The next thing I strapped down was the hood kickstand and the fuse box-engine coolant bottle also with no success on the noise. This is when I did some testing to try and find out more about the noise and first tested if it was rpm related, so I ran it up in 2nd above where it would be in 5th and could not get the rattle, I did this in 3rd as well to no avail. I then got it to rattle in 4th, again at the 65mph limit, and in 5th the same. This tells me that this is speed-related and my hunch is that it has something to do with airflow. The next day I took the windshield wiper cover off and was soon convinced that I found it as rattling the loose assembly around made the same noise, very similar to the rattle, and was in the area of which I heard it first. Unfortunately, after first packing it with a rag, then zip-tying it down, the rattle remained at the 65mph range.
On another side note, I tested running the ac in different modes from off to on, low to high, hot to cold, max to vent while this rattling was happening and it did not seem to hinder it at all.
As of now, I suspect it is something buried somewhere in the car and I cannot find it.
If anyone has any idea what may be causing this please let me know, I am moving in 2 weeks and would really love to be able to go over 60.
Thanks,
Greg

 

Does your XJ use a speedometer cable because it sounds like it could be the cable going bad.

 

You could always set it up on rear jacks just an inch or two off the ground and give it slow gas until you get to the 65mph mark and then see whats going on. Probably need 2 people, one on the gas and one looking in the engine bay. Be safe of course and stand to the side, not in front of the Jeep..... if theres no noise its either the front section of the drive train or it needs a load like driving to make the noise.
Really long screwdrivers, pry-bars, or breaker bars work well as stethoscopes. Put one end to your ear and the other end to somewhere on the area making noise. You will definitely know when youve found the noise if you cant see it because it will be much louder coming through the tool you use as a stethoscope. You can usually get to within a couple of inches of the problem noise with this method.

 

I will go ahead and give this a try to see if I can hear anything, a great idea on using the screwdriver as a hearing aid. I will make sure to get back on anything I can find.
Thanks

 

I am not sure if it does, what would it be doing if it was going bad? possibly spinning around somwhere?

 

After blocking up the car on some jack stands, I carefully put it in gear and started giving it some gas. I got it up to 75 in rear wheel with no noise and opted to then try it in 4 wheel high to see if it was related to the front axel, again, 75 no noise.
As I have become more observant of this rattle, it also ticks just a couple of times when coming to a stop around the 30 to 35mph mark, but only sounding like it bounced once or twice.

 

Upon doing some more research
the vehicle does have a speedometer cable, but it seems like that would be reflected on the gauge when it gets rattly.

 

I think I found it.



Aggressive rattle. Bad news!

 

not necessarily, if it is rattling against the body and not inside the cable itself, but since that didn't repeat the rattle in the static test you performed, then I would surmise that you have some type if wind rattle in the engine compartment. That is going to take a whole lot of Noggin Pokin and maybe a good strong leaf blower to identify.

 

I have figured it out, my hunch on it being speed-related seems to be correct as the culprit was a loose piece of trim around the windshield on the passenger side that rattled at 65mph. Thanks for everyone's suggestions and help.

 

HA! And here we are looking under the hood, checking driveline, scratching our nu... I mean heads. All for a piece of trim haha. Well, good catch either way!

 

If you ever need to replace your windshield, that'd be a good time to lose that aluminum trim. The later models use exactly the same glass, and the rubber trim used by later models will work perfectly.

And you may not have a choice. Finding the original aluminum trim might be pretty difficult. If you lose or damage a piece, you may not be able to replace it. The rubber is easy to get.