Eaton Fuller 13sp growling issue

you can pop your bottom plug--dont drop the oil---and see if there are any chunks on the magnet
if thjere are peices --you might want to drain it--and try synthetic---not sure if it will help--maybe get the guy who rebuilt to have a listen

 

May not be the trans. Check the air ride, ride highth. If its to high or to low it will cause a vibration or a growling sound through out the entire drive line and may sound like its coming from the trans.

 

If the noise varies or gets worse as go go over bumps or bridges/overpasses it may be the air ride, I had a bad leveling valve on mine, but it sure sounded like I was getting ready to lose a tranny!

 

Have the trans oil analyzed?
If there is chunks on the magnet it's too late, don't bother with the synth, find another trans.

 

In my older truck i had a RTO 12513, when it got rebuilt they put 50wt oil in which it recommended. I had use 90wt gear oil in the past, so with the thinner oil it would be alot more noisey, it ran great and shifted well but noisey

 

pull the plugs in both rears also, the noise will follow the drive line and sound like tranns and be rears.

 

if it was rebuilt with some new gears or parts and some of the original parts that will make it have a (growling) some trans are quiet some are not do a oil sample and if it has one watch the temp. another thing that it might be is the snapring on the back of the main shaft might of fell of letting the gears float more than normal.

 

Sae 50 engine oil and Api 90 gear oil are very close to the same vicosity, just rated with a different numbering system,(just to make things more confusing) gear oil has more anti wipe properties so it would stick to the teeth better, but that stickyness make for hard shifting.