With the clutch disengaged, or while the car is coasting at a low speeds while in neutral (below 20-30km/h) I can hear a rubbing/clicking that moves with the speed. So if I am going slower, the rubbing sound rpm is lower and when i'm going faster the pulsing is closer together. My 8.8" diff has Limited Slip.

Conditions:
-DOES NOT happen when in gear no matter what.
-ONLY happens when coasting.
- up hill coasting, I don't notice it
- car drivability is 100% still.
-car rolls great still.

Things I have done:
-changed rear rotors and pads
-put rear on jack stands, ran the car in 1st gear at idle and used a stethoscope to listen to the wheel bearing and rear differential for noise. checked out perfect.
-last year changed diff fluid with lucas 75w-90 synthetic gear oil and a bottle of AC Delco (matching spec to motorcraft)
- in July 2016 I changed the driveshaft universals to MOOG brand.
-bushing are good but I am about to install an energy suspension polyurethane kit

-Car is stock with stock gear ratios from factory.
-tires are 245/50/R16 and are new

It is a weird problem. Its a noise you can only hear on the passenger side and also quietly when the cab is closed during coasting. So, i cannot take a video cause its not loud enough unless I get a profesional mic

 

did some driving yesterday. Got going really hard. It drove nice! we slowed down and i got my friend to hear me coast at less than 20km/h with the clutch in and in neutral. They didn't hear anything but i can hear a metalic knocking that moves based on the tires rpm inside the cab. the cab makes the noise resonate from the rear. still don't know what it is.

 

is there anything in the tire, like a nail?

 

nope. no nails cause its new.

i took a video today of the cab closed.

I'LL TRY and post it sometime

 

so no noe really replied but I found the problem.

The diff (3.27 8.8 28 spline) has 136,000km and I have put 7,000km since hearing the noise the first time. Something has worn out and something chipped off the pinion gear that is really small, going through the bearings, ring gear, spider gears which is causing it to all be sorta loose. I'll posts some pics later. But basically, wear and tear, its time for a rebuild.

I'm trying to go to 3.55 gears since I do a lot of highway and FRP parts for durability. Will see how much a rebuild costs but its looking like a 1700$ canadian build with FRPP parts.

or

I'm trying to research if I can take a f-150 8.8" 31 spline rear end that I can get complete for 300$ and put it into my 8.8 rear end housing of my mustang. it has a 3.73 ring gear in it which I am ok with since I cannot beat the price here. plus 31 spline is better correct??

 

the carrier should swap in, the tone ring from the truck needs to be removed, and you will need new axle shafts, and of course the gears will have to be set up.

 

the conditions sound like pinion bearing, but the a clicking noise doesn't fit the bill

 

Thanks dude. I was just reading the same thing. haha. I've put in 12 hours of reading so far but your confirmation helps a lot.

 

its weird I know. However, the noise is getting slightly worse slowly. very slowly. 1% per week.

 

Similar issue happened to my brother's WRX. At first we thought it was rod knock, but it turned out to be a chipped tooth on the gear set for 2nd. It would make noise in neutral, but go away in gear. Open up your diff cover and look for debris.