Rear End Noise

[pintokid]

I was riding with my wife driving today and I noticed a kind of "roar" coming from the rear end under hard acceleration. I know that is the only time on a dry road that the AWD activates power to the rear. As soon as she backed off, the sound was gone. It is definitely in the rear, not where the PTU is located, and only under acceleration. Has anyone seen this before. We have about 62K on the 2017 Edge and PTU was replaced at 10K and no other transmission fluids have been changed.

[enigma-2]

Either the rear differential or rear wheel  bearing. Both create a roaring noise on acceleration, but the differential will also create a roaring under additional load.

 

The differential could be failing if its leaking, running low on lubrication, or you drove through deep water at some point, allowing water to enter the axle, causing lubrication failure. Another possibility is the car was subjected to a towing overload at some point. 

 

One method to isolate between the two, would be to lift the rear end and shake to rear wheels. Also rotate the tires while listening to the bearings. An old mechanics trick is to use a long, wood handle (plastic works as well), the slot end on the area of the bearing with your ear on the handle end. Listen for grinding.

 

In either case, something is wearing out in the rear. 

 

Have you ever changed the rear differential fluid? Best to do this every 60,000 miles or any time the car has been driven through deep water (level over the rear axle). It's in the cars  maintenance manual (at least in mine for my MKX). 

[pintokid]

The car has 62K now and needed a front wheel bearing at about 10K. Thanks for the advice. The car has had an easy life. Only light towing last year a few times. Never been through deep water. The car needs to be back at the dealer for a recall, so I think I'll get them to change all the fluids (except engine oil).

[pintokid]

The dealer tells me it needs a new PTU. $3200. Not a surprise actually but still disappointing. This will be the 3rd PTU in this car.

[pintokid]

I complained about the cost to the service rep and he gave me the phone number to complain to Ford. They were polite but very quickly replied they could not help. I assume because this is not a pervasive failure in the Edge. Oh well.

[DonWar]

I know that your letter was from 3 years ago but I was wondering if you replaced the PTU again and if it was the cause of the problem. I bought a used Edge from a Ford dealer and the PTU was leaking when I bought it and they knew it but said they were waiting for the part. They replaced the gasket but it turned out the PTU was bad so it was replaced under warranty.  The car had 119,000 miles then and now has 157,000. I have the roaring noise in lower gears that seems to be coming from the rear. I brought it to my mechanic suspecting it was either the differential or a wheel bearing. He said it was the differential and said it was low of fluid and they drained and changed the fluid. The noise did not go away so now I am wondering if it is possibly the transmission? It seems to shift fine, no slipping.  Or could it be the PTU again?  Did replacing the PTU fix your problem?

[enigma-2]

When my PTU needing replacing, there was a muted roar type sound coming directly under the front seats. 

 

A roaring noise from the rear end is  usually worn wheel bearings or differential ring and pinion gear issues in the RDU. Your mechanic found it was the RDU and refilled the unit. But the damage is done. You can't fix worn gears by just replacing the fluid.  You will need to have your mechanic disassemble the RDU and visually inspect the RDU.