I have a weird whining noise from under my truck at first I thought it might be from my starter since its been messing up on me and the solenoid is going out as well as hearing the teeth from the starter and the flywheel which made me think maybe the wheel on the starter is going bad also but I found a video of a guy diagnosing bad pinion bearings in the rear Axel and since my pinion seal is bad cause the u joint and saddle is wet as well as the bottom corner of the gas tank that it might be that. Figured I'd ask some opinions since I'm getting busier at work now and don't have alot of time to play around. Just need it fixed....

 

Not the axle but the differential....

 

When do you hear the noise?

 

After I get up around 40+ and it's only really noticeable when I accelerate

 

Yeah, that sounds a lot like a pinion bearing. If you catch 'em quick, you can just do the outer, and seal, and call it a day. Leave it too long, and it can get REALLY expensive. How long is too long? That is a very good question, and there is no good answer for it.