High pitched whining noise

[southernzr5]

I have a high pitched whining noise coming from what sounds like under the back seat area while driving. You can't really hear it till I get to about 45-50 mph and it goes away when I let off the gas pedal. I replaced my rear axle fluid a couple weeks ago and didn't notice any unusual signs of wear. I thought it might be the fuel pump, but wouldn't it make that same noise at lower speeds? Truck is a 2003 zr5 with 137k miles.

[southernzr5]

I'm thinking now that it might be in the transmission. When I start off in 1st and gain speed it almost sounds like an airplane taking off. If my trans is on its way out, what would you recommend as far as replacement. Anyone had any experience with Monster Transmissions? If I get it rebuilt should I look into any shift kits or servos? Just trying to plan ahead.

[southernzr5]

anybody?

[Torskdoc]

Sounds like the Rear end is whining. On load whinning (accelerating) with the whining going away when coasting or de-accelerating is indicative of pinion and ring gear mis alignment, or worn pinion gear bearing/shims. My 95 Jimmy whined like this from almost day 1 all the way up to 126,000 when the bearing finally let go. Find another S-10, Sonoma, Jimmy, Blazer or Bravada with the same gear ratio and swap it out. Install NEW U-BOLTS with the Axle.