Which model and year are you talking about? My 05 Highlander 3.3l specs 80W90 GL-5 for TC and Diff. Changed the fluid at 38,700 miles for the first time with Shell Spirax HD 80W90. Virtually no noise.
Sam
...Differentials have been living 200,000 with 80w90 Dino gear oils & no maintenance since the 60's.
+1
..... and without whining noise whenever dino oil is replaced according to OEM schedule in the old backwards days.
Sadly gear train whining noise in today's applications seems not uncommon, despite use of modern base oils and additive package in modern day manufacturing gear train products...... when CAFE possibly is a consideration.