Howdy!

Long time lurker; this forum has helped me a ton, but this one is stumping me. I took the Jeep to a muffler / custom exhaust shop to get the header welded up and the motor mounts replaced. After they did the job, it’s making a grinding / scraping sound when I let off the gas, sounds like it’s right near the driver’s side foot well.

It’s on a 2-3” full OME kit, but wasn’t making the sound before this work was done, so I don’t reckon it’s drive train related but who the hell knows.

Shop is closed this weekend, but before I take it back there wanted to get any ideas from y’all.

Thanks!

 

I'd have a look at the mount down there, (I haven't changed the mounts on mine yet so take this with a grain of salt.)

I'd guess when you let off the gas, the engine moves and is potentially scraping on something due to an issue with the mount.?

 

Most likely the exhaust is getting against the body pan / frame rails somewhere due to torque twist when decelerating. If the exhaust was fixed before the motor mounts were replaced, it may have looked great, but then ended up 1/4” away from something when the motor mounts were replaced.

 

Thanks y’all, that makes sense and helps a ton.

 

Very close quarters at the trans cross member.

 

Get a friend to jump in and rev it up whilst you look underneath too 👍

 

In Park of course

 

Hah! It doesn’t make the sound while it’s stationary which makes me think it’s something rubbing against part of the drive train that’s in motion when the Jeep’s in motion (sorry I’m still pretty new working on cars in general), and it only happens when I let off which makes me think it’s something exhaust related, or something else that might settle when not under load.

That transmission cross member, that’s about halfway on the Jeep right? Exhaust feels pretty solid there. It really does feel like it’s coming from right under my foot.

We’re heading off on a 2200 mile road trip and I’m worried about this one since the scraping sounds so severe.

Thanks to everyone for the help so far.

 

Try rocking the engine by hand see if you can get it to reproduce the scraping sound. There's obviously movement somewhere, most likely the exhaust or engine, since they were fine before hand.

I once had a saturn make a lot of cabin noise when idling but would almost go away under load. When diagnosing it I could rock the engine so much that it would make contact with stuff. Changed the mount and solved it. When under load, in my experience, the engine doesn't move nearly as much when theres no load.

Maybe it's the same with jeeps 🤷‍♀️ maybe somehow got a faulty mount put in. Wish I could help more but I got my first XJ a couple months back and it's mainly sitting on the drive whilst I make my way through a list of maintenance repairs lol.

Also see if the exhaust is making contact with anything anywhere.

If possible see if you can upload a video to youtube of the sound so we can get a better idea

 

Here’s the sound. I can’t reproduce it by rocking the engine, it only happens while the Jeep is moving.


It also rattles a bit sometimes when letting off the gas. After some investigation that’s the transmission (not the exhaust) rattling against the crossmember. The sounds seem related as the scraping stops when the rattling starts. I wonder if the transmission mounts need to be replaced as well, maybe something is off kilter now with the new engine mounts? Not sure what would cause this scraping sound.

 

Ok, so I've done some more brainstorming.

Here is the scenario so far.

No noise when idle.
-Moving Parts when idle.
Engine
Exhaust
Trans?

Noise when driving
-Moving parts when driving
All of the above +
Suspension
U-Joints
Drive Shafts
Etc
Only other noise that I could think of coming from the exhaust would be that perhaps the bolts are loose on the flange causing it to move.

But I'm going to say that you've examined the obvious suspects for now and move on to less obvious suspects.

Perhaps the noise isn't related to the shops work. Are you driving the jeep any differently than you were before you picked it up?

For example, is there now ice on the road, and you've started driving in 4x4 where as it was in rear wheel drive before? Could this be a front U-joint issue?

Perhaps one of your suspension springs have given up and broken, and now its rattling around as you drive about.

What I would do next is jack your jeep up with 4 jack stands so that the wheels are off the ground and see if it still makes the noise when you drive it. And do the same as before, get a buddy to drive whilst you VERY carefully look for the source of the noise. Stay away from moving parts!
Other than that, the shop opens tomorrow lol.

Let us know what the problem was!

 

Took it back to the shop and they banged their heads against it for a bit. Re-did the transmission mounts and added a couple of washers to the cross member and all’s well. Did some adjustments on the exhaust line all the way down the back to make sure everything sat level, and now everything is so soft and smooth it doesn’t seem like the same Jeep.

My mounts were sagging so bad that replacing them pulled the engine up where it belonged, which seems like it tilted the exhaust and transmission down a bit.

 

Hehe, the mounts were my first guess, glad you got it sorted!