I recently bought a 1999 Jeep Cherokee Sport 4.0L.

I love it, but my one complaint is that at highway speeds, 70mph+, it has a fairly loud humming noise. It's loud enough to give me a headache after a 5 hour drive. The noise sounds like it is coming from the front somewhere, maybe the engine is just loud at that speed? When I release the gas pedal the noise gets much quieter, and then resumes as soon as I hit the gas again. It sounds like a single engine airplane or something.

Is that normal? Are these just loud at highway speeds?
I have replaced the front brake pads and the tires.

Thanks!

These things arent the quietest vehicles on the road but it's hard to give you an answer based on the info you have given. ANy way you can take a video so we can hear it.

Is it normal for there to be a noticable amount of engine noise once you get past 70mph? That's all I was wondering. Would I just put a video on youtube and then post a link?

It have oil in it?

It has fresh oil.

a little bit of noise is normal but i dont think you should be getting a headache from it thats not too normal

It's pretty loud. I'll try to take a video. Is there a way to put it on the website here?

I was told by a shady mechanic when I took it for an alignment that my tie bar needed replacement and they couldn't do the alignment. I didn't trust them so I haven't pursued that yet, I'm not getting any vibration or anything. Would that play into this at all?

I was researching a bit and saw that wheel bearings can be loud at highway speeds when they are going bad. It's got 150,000 miles so that could be it too. Does anyone have any experience with that and could you describe the sound?

Yeah, headaches shouldn't happen. My '91 4.0 makes its series of noises (it's a noisy engine, just gotta distinguish between what's good, normal, bad, sorta-bad-but-ok, etc.), I have a high flowing 2.5" exhaust with a Flowmaster Super 44 muffler and high flow cat. I also removed the silencer in the airbox, and I don't get headaches. The noise is actually nice and aggressive (the good noises I mean lol).

Sounds like bad wheel bearings to me

So what does the noise sound like I was thinking exhaust leak

the sound changing with the gas pedal makes me think exhaust as well

the sound is a very steady hum. It sounds like a loud engine, I just haven't ever had an XJ and don't know if it's supposed to be this loud. It is the factory exhause. I crawled under and eyeballed it at lunch and it looks good all around, not a lot of rust and no visible holes, but that was just a quick visual inspection.

Wheel bearings might be something to look at. Would they stop humming when I let off the gas though? and wouldn't I get a squeak or something at lower speeds? I do have a slight pulse when I put the brakes on. I got new pads last week (on special so the labor was only 20 dollars more than it would have cost me to do it. Otherwise I would have done it) and thought they might have done something wrong. I was going to have them double check it this week.

When my stock manifold cracked, it was more of a loud collapsed lifter kinda ticking noise. Is there a loud hum related exhaust noise possibility? Highway is what gets me. Every vehicle I've owned, if their was a suspension problem, it made noise at highway speeds.

Maybe you have an aftermarket exhaust with a heavy drone?

If letting off the skinny pedal immediately changes the tone then it is emgine related not wheel bearings. Your actual travel speed would have to change to make a bearing sound change. When you are driving along, lift the accelerator, throw it in neutral and mash it a few times to about 2500 rpm and see if that duplicates the sound. If so I would lean towards exhaust as well.