One problem related to differential unit has been reported for the 2001 Toyota Highlander. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2001 Toyota Highlander based on all problems reported for the 2001 Highlander.
Harmonic noise from beneath car at 30 mph with power applied, similar noise, of lessened magitude at 60 mph. Dealer replaced rear differential and then transmission. Noise remains. Dealer says Lexus rx300, with same transmission, has had same problem. Unknown cause as yet.