Lots of things can cause a knocking noise.
However, in this case, if there was no knocking noise until you put in the 87 octane gas, then the knock is caused by abnormal fuel combustion, called "knock" or "ping".
All engines will mix fuel and air in a 'fog'. Then this 'fog' is compressed and ignited. The more the fog is compressed, the more energy can be extracted from the fuel.
Normally, the fog will burn quickly after being ignited by the spark plug. However, if the fog is compressed too much, it will explode, sometimes before the fuel is ignited by the spark plug. This explosion is heard as a knock or ping sound. A bit of knock does no harm, but extended periods of knocking may damage an engine.
The expensive, supreme gasoline can tolerate more compression (before knocking) than regular gas. Your engine is probably compressing the fuel beyond the tolerances of the 87 octane. So fill up with the supreme and you should be fine.
BTW, your engine has a device called a 'knock sensor' that detects knock and adjusts the ignition system to somewhat compensate for poor quality gasoline. If you are hearing a lot of knocking, this sensor may not be working.
However, you should always use supreme gas in your Land Rover. It may cost more, but often some (but not all) cars get better fuel economy using supreme. For example, my '97 Cadillac gets 15% better fuel economy by using supreme, which more than offsets its higher price.