Hi.

I am experiencing rear end noise.

It sound like a mix between grinding and light popping. I'll see if I can't record it and upload it.

I can barely hear it when the car is cold, but after a couple of miles the sound appears at low speed(goes away at speeds above 20mph). This is for short trips btw.

On long high speed trips I don't hear anything until I slow down. Last time I went for a 30 minute drive at 75 mph the grinding started when I reached 35 mph and got worse the slower I drove. Then I parked for 15-20 minutes. On my way back the grinding was much worse, I could hear it all the way ip to 60-65mph, it went away after a mile or two though.

I know there must be something very wrong somewhere, but I have no idea where to start. Any tips would be great.

My specs;
Dana 35 LSD
4.0L w/AW4

I changed the fluid almost 2 years ago and it is pretty brown again, I am going to change it next weekend.

Thanks

 

Start with the U-joints. Check to see if your pinion yolk has play in it.
leaky pinion seal can also be a sign of a wearing or worn out pinion bearing.

 

How much play should there be in the yoke?
Where do I check if is leaky? On the front side of the diff? Also do I have to take it all apart to check for worn bearings?

 

There should be no play in the yoke. The yoke has a seal, If it is leaking it should be obvious and have gunk build-up around the seal.

My first guess is rear wheel bearing. Lift the rear axle, spin a tire and feel and listen for resistance or grinding. Try to move the wheel up and down,side to side. Any play or clunking is a worn bearing. Keep in mind the wheel can move straight in and out about 1/16 or 1/8 this is normal for a c-clip axle.
The wheel bearings are supplied lube from the diff pumpkin. If the levels were low or the fluid sour than the wheel bearings were probably starved for oil.
Wheel bearings are easy to replace and inexpensive
Lastly, if you cannot any thing obvious. Remove the diff cover and inspect.