Can't figure out!!! Still Baffled by growl when first moving forward

[Will Cunningham]

Ok, here is what I suspected and fixes applied so far.

Suspected a bad IWE and/or hoses. Replaced both IWEs and all hoses and check valves to IWEs all the way to the solenoid. Solenoid checked out per TSB guidelines. After replacing the hoses and check valves, the vacuum levels at all points meet or exceed TSB guidelines. Still have the 'growl' when first moving or turning at low speed and low rpm. Replaced both front hubs even though they seemed ok (94k miles). Then applied TSB 22-2219 which basicially allows the 4wd to be available without waiting for the IWEs to engage. The vacuum lines are capped off, so the IWEs are always engaged at the wheel hub. The 4WD would be activated through the transfer case.

I still have the low 'growl' when first starting or turning, but goes away if the rpms are higher. Worse if I am turning uphill at low rpm( going into my driveway) even after driving 5-10 minutes. It sounds like the IWE is trying to engage, but I know they are already engaged in the hub. The transmission was serviced about 5,000 miles ago(Ford Dealership that has a very good reputation), so I am wondering if this must be transmission related. I have not checked the tranny fluid yet, but am suspecting it may be a little low.


Bugging the heck out of me, plus growling noises usually are not a good sign. May have to take to the dealer. No codes showing anywhere either.

Any help and suggestions would be greatly appreciated!!!!

 

[Will Cunningham]

Update
Checked the transmission fluid when cool and will check when warm as recommended. The fluid was up to the top and almost running out of the dipstick hole, so think it is full. Showing overfilled on the dipstick, but again, checked when cool.
Transmission seems to shift well in all gears. The first start of forward movement is normally the most noticeable noise.

 

[99WhiteC5Coupe]

Update
Checked the transmission fluid when cool and will check when warm as recommended. The fluid was up to the top and almost running out of the dipstick hole, so think it is full. Showing overfilled on the dipstick, but again, checked when cool.
Transmission seems to shift well in all gears. The first start of forward movement is normally the most noticeable noise.

You did not post the year, make and model - I’m assuming it is an Expedition.

Do you have hydraulic power steering or an electric power steering system?

Over the years, a growling noise often was a result of a power steering pump issue (pump or dirty fluid).

 

[Will Cunningham]

Oops, 2016 Ford Expedition EL Limited with 3.5 liter turbo ecoboost engine, 94,000 miles, electric power steering 4WD

 

[Will Cunningham]

Problem seems solved by adding the Motorcraft Friction Modifier additive to the rear axle. After describing everything I had replace and troubleshooted, he told me it was probably the limited slip rear differential was not working the way it should. Adding a $15 bottle of the additive to the rear axle seems to have fixed the issue.

Had already replace a lot of parts and most needed replaced, but probably not all.

 

[adamsdaddy]

I didn't know a limited slip was an option. I have a 2016 Expy 4WD that likes to growl.
Hope to sell it and the popup trailer soon and get a Subaru. Hotel/motel stays now vs camping when younger.