It needs a 5-90 tune-up. Low miles means short trips without the motor ever getting loaded properly. It probably has deposits in the combustion chambers from too much cool running. The deposits are glowing red in there and under higher torque loads--low rpm more pedal, the spark plugs start the combustion, then when the pressure is going up, but before the charge is fully combusted, that glowing deposit starts a small semi-diesel effect that pops off and makes that knock.
I don't know if that makes sense to you, but the cure is to make sure you run the motor hot once in a while, which is the 5-90 tune-up. 5 miles at 90mph. You want to burn up the deposits. there are chemicals, by Lucas oil and others, that are supposed to help this. I don't know, though. I wouldn't want to break anything loose in there. I would just drive it harder and at a faster engine speed and see if it goes away.
Torque is basically how much fuel can you burn in one revolution of the motor. Torque is pressure and heat. Driving a car on short trips only means you never get that heat you need to burn up all the garbage in the gas. Once you have that garbage deposited in there, the pressure and heat you need to burn it away can also cause that semi-diesel effect. So you have to ride that line so you don't damage the engine.