I have a 2002 ford ranger 4 wheel drive V6 4.0. I noticed my tfront tires were wearing un even. The outer edge of the tires were so bad they were smooth and moving towards the inner part of the tires were more normal. I had a loud humming sound coming from the front end. (it sounds like the engine was not engaging to 4ths gear. Almost like a high mmmmmmmmmmmmmmmmm sound) I just figured it was becuase the tires were warn so bad and the dealer agreed. So I had 4 new tires put on, front end alignment and new breaks. Was so excited to finaly think this annoying sound was going to go away. Well driving my vehicle home the sound was still there. So I take it back to the dealer and they tell me I have a bad wheel hub bearing on the front left side. So I replace this and the sound is still there but not as bad. So Im thinking the wheel hub bearing was fine and the problom was something else.
before I replaced the wheel hub bearing the sound was constant and started as soon as I was pressed on the gass and got louder as I went faster. Then when I slow down the sound gets lower and lower until I come to a complete stop. Almost like an electric car sound.
Now after the new hub bearing is in the sound does the same thing but not all the time. If Im at a stop sign and I start moving the sound starts hmmmmm and then as I go faster it continues hmmmmmmmmmmm and hmmmmmmmmmmmmmmmmmmm if you get my point. But sometimes I drive now and it sounds normal but only for a few times before I stop and then it starts making the hmmmm again.
I was paying close attention to my RPS to make sure the transmission was ok. It appears to switching gears fine but sounds as if the truck was in third gear at 65 miles an hour instead of over drive. But at 65 miles an hour my RPS were only at 2100 and if the truck was not completely shifting to the over drive gear I would be at higher RPS. So thinking this sound was coming from the engine not swtiching to the highest gear does not make sence. I when my truck is idle it sound fine. This sound only happens when Im moving and the faster I move the louder it gets. What could this possibly be.
Please help me the dealer and Mike tire plus needs to find a new jobbecuase they just keep costing me more money to guess what the heck it is.

 

I've heard a couple V6's do that. A bad hub bearing wouldn't make a high pitched hum - it's more of a hollow grinding sound. In some cases it could be the electric cooling fan. It might not kick on sometimes because of the temp. gauge. Then again, I always suspect the fan...

 

well I did have that sound also but after replacing the hub bearing that sound went away. But the sound im talking about is almost the same but gets louder as I press on the gass. This is not a fan issue because the fan would not get louder as I press on the gass. I may not be explaining the sound properly. It over powers the radio and is bugging me. it sounds like the engine is reved to high when Im driving. and as I slow down the sound get lower. But this is been doing this for 2 years and still can't figure it out. If something was bad in my truck surly it would have damaged by now.