A gearbox hum or whine at highway speed is often fluid, bearing, or transfer-case related.
Here is what to check first and when to stop driving.
What that highway whine is telling you
A humming or whining noise from the gearbox at highway speed on a Land Rover Range Rover V is one of those symptoms that rewards early attention. It can come from the transmission itself, but on these vehicles the transfer case, differentials, propshaft, or even a wheel bearing can sound like gearbox noise from the driver's seat. If the pitch rises and falls with road speed rather than engine rpm, suspect driveline components; if it changes with gear or torque, the gearbox and torque converter move up the list.
Read the full breakdown in the Knowledge Base
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