A few weeks ago a humming noise started accompanying 4wd on speeds 20-55 mph. I've driven 4wd Rangers since the mid 90's and I've never heard a difference between 2wd and 4wd. It's most notable when I take my foot off of the gas and it feels as if there might be some resistance to coasting, but not sure. I changed both front and back differential fluids and also the transfer case transmission fluid. All fluids were really muddy, but none were very low at all. Any thoughts as to what this humming/vibrating sound might be coming from?

 

Welcome to the forum

Year of Ranger would help?

2001 and up have full time locked front axles so shifting to 2WD wouldn't reduce a noise if it was front axle related

Earlier had Automatic hubs or manual lock, so would matter if noise goes away in 2WD

 

Thanks much. It's a 2009 with 117,000 miles on it. No heavy loads or towing in 4wd, or only rarely and not recently.

 

So you have Live Axles, always locked front hubs
That means front axles, differential and front driveshaft are always engaged, spinning when vehicle is moving

2WD or 4WD is done solely in the transfer case
It's possible the front differential ring and pinion has some play, so causes a hum when power is applied to driveshaft, no, or much less, hum when axles are driving the ring/pinion

Nothing jumps out at me

 

Thanks for checking this out. I'll be off to the dealership. Maybe it won't be a big deal, but I'll let them get hands on it just to make sure.