Grinding sound when accelerating...

I have a 2010 Limited Flex 5.7L V8 with just under 200k miles on it.

It's a workhorse for me and I love it. Recently I have heard a (metal) grinding sound when accelerating, more prominent in 2nd and 3rd gears. I just drained the rear diff fluid and am picking up the cover gasket today so I can clean the inside out and check for metal shavings. The drain plug did have a good amount of goop on the magnet, and the fluid was medium-dark brown. I also bought new crush washers to replace the old ones, but I have a feeling it may be something other than the rear diff. The grinding is a rotating sound, not constant. I figured it's probably due for a flush on all fluids, so I'm going to hit the front diff next, transfer case, then transmission.

I'm also swapping out my rear rotors and pads which still have quite a bit of life to make sure they are warped or something weird.

Work done in past 2 years:
**Replaced L CV axle after a boot exploded from road debris, but didn't change out the gasket seal. Haven't had any issues but will probably pull it off when I'm doing the front fluids and replace both seals.
**Changed out front rotors and brakes last month, then topped off brake fluid because the caliper connecting brake line snapped when I accidentally dropped the caliper... oops. Bled out the air and connected back to caliper. Bought new connecting lines for all 4 brakes, replacing as I go.
**Just completed routine oil change couple days ago, pretty black after 6k miles (royal purple) and feel like there could be a tiny leak coming from somewhere.
**I did have to replace the dipstick O-ring last year after a bunch of oil went everywhere the same time as my CV axle boot blew, so I thought it was residual grease.
**Replaced the transmission fluid cooler after someone backed into my truck with, I was shopping or something... I noticed it when I cleaned up the CV axle boot grease. Front bumper is a modular bumper made by Vijay?, but designed without the TFC in mind! Shaved down the front bumper to give room for TCF.

 

Sounds like the transmission slipping. I would start with drain and fill. Take it to autozone or oreillys for a full scan including transmission codes if you don't already have one that does.

 

When you say rear differential cover gasket, what exactly do you mean???

 

Does it make noises in park while running? Y, remove belt and see if noise still there. N, check driveshaft carrier bearing. Jack up the rear of truck while chocked at the front and put in N. Turn off key, Rotate tires and driveshaft while trying to wiggle them around and listen for sounds. Report back with your findings.

 

Is that not what it's called? That's what I found online... housing gasket?

 

No only when moving, mainly when accelerating. I'll have to check driveshaft bearing, looking at the center support bearing between the two driveshafts, is it supposed be well greased?

 

Looks like there might be a transmission pan gasket leak... might be the issue.

 

If you've never done maintenance on the transmission... it's time to start. I started getting the same transmission issues about that mileage. Either OEM or aftermarket, just start niw before it gets worst.

 

No, it is sealed with a rubber support between the bearing and the clamp/housing/hanger. The splined slip yoke should be well greased as well as u joints.

 

the issue or not, trans fluid loss is bad news. Get it filled!

 

If it's the rear right axle bearing/wheel bearing, should I just replace the bearing or buy a complete housing?

 

These Toyota axles do not have diff covers. Changing the fluid is done through drain and fill plugs on the diff housing. The third member is removable from the driveshaft input side and has a gasket associated with it. Only need that if you’re pulling your third member out for some reason. I didn’t see where that was your plan.