mine started at 20k. Alternator bearing is whining. I just tell every one it has a super charger. LOL BTW now at 125k. still whining, still works.

 

This could be ANYTHING attached to the belt - but my money is on the alternator.

BTW - only whine I have ever heard in my truck used to come from over on the passenger seat side. But I fixed it right up - got me a divorce...

 

check the torque converter and transmission. Unbolt it from the flywheel and push it away, start the engine and rev it up a little. If the noise goes away, it's on the tranny side, If it's still their, It's on the motor side and you have ruled out the transmission. If it goes away, It's the transmission.