Rotational noise between 50-55 MPH

[Alex05]

Issue: Between 50-55mph, if I let off the throttle, and then get back on at very light throttle, I can hear a noise that seemingly is coming from the transmission tunnel (perhaps the bell-housing?). The sound is as if there is a nut bouncing around inside the bell-housing. I don't believe there actually is a nut bouncing around inside the bell-housing, this is just the best way I can describe it. The noise level is such that if the radio is on, I typically can't hear the noise.

I only observe this issue between 50-55mph. I can make the noise stop by applying more throttle.

My ATF in this '05 Unlimited has potentially 15 years of life on it and 23k miles.

Any thoughts? Is this perhaps expected behavior around the point when a lockup torque converter unlocks? I'll be the first to say that is pure speculation on my part.

I'm considering just flushing the transmission and re-testing, though the fluid does appear ok.

 

[pagrey]

I have an 04 and here's my take. The flex plate bolts can come loose, that's bad. Your issue probably is not those bolts but they can be checked through the access plate in the bell-housing. The 42RLE does what's called PMMT or partial lockup of the torque converter by pulsing the solenoid and it can make an awful rattle that sounds a bit like you describe. It is normally very noticeable when you have your windows open and are driving next to a wall or high curb. Mine has done it since 30K and still does it at 140K. I don't think it's a big deal. As always make sure you only run ATF+4 and have the level correct. If the noise gets worse check the flex plate bolts. Some people around here really like to flush the fluid, it will never fix a broken transmission. I think the factory schedule is fine but if you have money to burn flush away.

 

[Alex05]

Thanks for the detailed reply. I'm only the 2nd owner of this LJ, and I'm reasonably certain that it's ATF is 15 years old (i.e. from the factory) and has 23k on it. While the mileage is certainly not yet at the scheduled replacement interval, 15 year old fluids are...15 years old. I've already replaced every other fluid; I may as well replace this one and while it's in the air, I can inspect the flex plate bolts, just to be sure.

 

[pagrey]

While the mileage is certainly not yet at the scheduled replacement interval

There is no replacement interval for the fluid. The only recommended factory service is to replace the filter. There are not even instructions in the service manual for how to change the fluid. The few quarts replaced in that service are just because you drop the pan. A dealer serviced 42RLE would still have a good portion of the original fluid well beyond 200k miles. Most people don't worry about what the factory recommends, do what makes you happy.