The Nissan Path

Hi,

past few months I can hear low frequency pulsating humming vibration/noise when driving over 60 mph highway.
It stops if I put in neutral.

Not related to A/C, ventilation.
Not related to highway, any highway is good.
And it does not cause any vibration, although it sounds much like one.

How to describe the noise?
It's barely heard, if you do not know what to listen, you won't distinguish it from all other driving noises. Maybe it sounds very much like TIRE noise, but it's pulsating.... 2-3 seconds it humms, then it fades out for 2-3 seconds, and repeats as long as I drive 60 mph or more.

Any idea?

U joints?
If you're putting it in nuetral should be like if you're letting go of the accelerator. From experience it sounds like u joints.

If it doesn't do it revving it in park is has to do with anything after the trans. Cvs
Hubs
Driveshaft unbalanced
Ujoints
Unbalanced tires.
If not it could be something with the exhuast mounts or isolators.

Hmmm... what bothers me most is the very constant interval of huming noise coming on and off. It's never always on, but it's always 2-3 seconds on and 2-3 seconds off (at 70 mph, for example). It never hums constantly, always comes up and goes away in 2-3 seconds intervals.

Tires? I guess they would produce constant noise.
All joints....maybe.

What I also thought it might be the BALANCING SHAFT on the bottom of engine. It's driven by preset loaded spring and maybe that spring tension got lost by the time and it's pulsating.... while it immediately cuts off when put in neutral.
Could this be the cause?

If you think its engine related you can just have someone rev it while you listen around.

Hmmm... I swear I uploaded this video few days ago on the forum, but cannot find it anymore. So let's do it again.

Here's a short VIDEO of how squeaking sounds like when going uphill or downhill:
https://www.youtube.com/watch?v=MzofzQvsmRk

When only maintaining speed on highway, squeaking is not heard.

It was driveshaft U-Joint, bad and totally seized. :/

After 3rd U-joint replaced, I become master. Now until I forget, I can replace one in 30 minutes, hehe