Water Noise When Radon Fan is On
We had the same thing happen to our system.  During the winter, water accumulated under the concrete where the radon pipes went into the basement slab and totally blocked the air flow causing our radon levels to go up. We have a 24/7 radon alarm that showed the higher levels.  We ordered a new fan but that was not the problem.  We cut the pipe near the basement floor and installed a "y" with a clean out cap and used this to pump out the water with a small pump.  The pump had to be primed first but after removing 15 gallons, the radon pipes no longer gurgle. Be sure to put the clean out cap back on!