Just bought my first Ranger today. A 2006 2WD XLT Automatic 5-speed with overdrive and cruise control. Has under 19 K miles. Looks spanking brand new; not a scratch or dent and beautifully detailed. However... ( ! ), I notice a high pitched whine or hum at hiway speed (well, above 30 mph) which disappears when I take my foot off the accelerator. At first, I thought it was tire tread noise until I let it 'coast' a bit. (Noise disappears when coasting, returns when I put foot back on the gas).
Ideas what to look for?. Does not seem to be on only one side, either front or back... just "underneath somewhere". Am I just being picky? Is this sort of noise normal for this vehicle? I am a newbie with pickup trucks.

That sounds distinctly like rear differential whine.
First thing you should do is have the axle fluid level checked.
If the fluid is low, find out where it's going. If it leaks out the axle seal and gets onto the brake linings, you're in for more problems quickly.
If the fluid level in NOT low, then the diff and or bearking need attention.

Get the fluid level checked and let us know.

Thanks, Captain Rich. I shall get on this and see what the fluid level is and have them check the seal, etc. I suspected it might be something like that. I'll get back with what I find out. Fortunately, there is a warranty on the power train :)

That sounds distinctly like rear differential whine.
First thing you should do is have the axle fluid level checked.
If the fluid is low, find out where it's going. If it leaks out the axle seal and gets onto the brake linings, you're in for more problems quickly.
If the fluid level in NOT low, then the diff and or bearking need attention.

Get the fluid level checked and let us know.

Captain Rich--- you were very close. It was determined today that the noise which annoyed me was due to a faulty pinion. They are replacing the offending part next Tuesday (under warranty) and I am looking forward to a quiet truck. Thanks for you time, effort, and advice. I do appreciate your answering...
Selwoc in WA state

Have the differential filled with 75W-90 Mobil 1 Gear Oil. This should help ensure trouble-free operation.

Just bought my first Ranger today. A 2006 2WD XLT Automatic 5-speed with overdrive and cruise control. Has under 19 K miles. Looks spanking brand new; not a scratch or dent and beautifully detailed. However...( ! ), I notice a high pitched whine or hum at hiway speed (well, above 30 mph) which disappears when I take my foot off the accelerator. At first, I thought it was tire tread noise until I let it 'coast' a bit. (Noise disappears when coasting, returns when I put foot back on the gas).
Ideas what to look for?... Does not seem to be on only one side, either front or back...just "underneath somewhere". Am I just being picky? Is this sort of noise normal for this vehicle? I am a newbie with pickup trucks.

NEXT QUESTION: Gear ratio. <1> Where on the rear end does one look to determine the gear ratio? And, <2> What is the OEM gear ratio for a 2006 2WD Ranger 5-speed auto with overdrive on a 4.0L V6? Someone said mine is a 3.55. <3> what would be the effect of putting on a 3.73, or maybe more? Thanks!
Selwoc
:p

There may be a metal tag on the differential. Ford often provides a ton of vehicle information on a sticker on the inside of the driver's door. Another way to find out may be to enter your VIN on the Motorcraft web site and search around:

MOTORCRAFT® FULL LINE CATALOG OF PARTS FOR FORD, LINCOLN OR MERCURY VEHICLES (http://www.motorcraft.com/catalog.do)

The vehicle certification (VC) label is located in the driver door jamb. The first 2 digits of the axle code indicate the rear axle and the third digit refers to the front axle, if so equipped.

17621

The vehicle certification (VC) label is located in the driver door jamb. The first 2 digits of the axle code indicate the rear axle and the third digit refers to the front axle, if so equipped.

17621
Captain Rich
OK, the two digits on my label say AXLE 95 . How do I interpret this?
Selwoc

The vehicle certification (VC) label is located in the driver door jamb. The first 2 digits of the axle code indicate the rear axle and the third digit refers to the front axle, if so equipped.

17621
Captain Rich
OK, the two digits on my label say AXLE 95 . How do I interpret this?

The metal label attached to the differential case says:

733 8 v 3 55 88 5Hr8

Decode please?
Selwoc

Take that information and call your local Ford truck dealer. They will decipher the code for you. I've had to do that several times for friends.

88 = 8.8 inch ring gear

3 55 is likely 3.55:1 gear ratio