when riding agressive through the forest i notice alot of gurgling noise from the rads when i stop to take a rest. I tested my rad cap and it was in limits and i change the antifrezze ever year I'm stumped.
Maybe it's jetted too lean.
Have you used a radiator flush to remove mineral build-up which lessens cooling ability?
Have you changed the crank seals within the last two years? If not then you could be losing pressure there and creating a lean condition.