... I HAD TOLD MY DEALER'S MECHANIC THAT I THOUGHT IT WAS COMING FROM THE STEERING CONTROL BOX - HE TOLD ME - NO CHANCE OF THAT - BECAUSE THIS VALVE HAS NO MOVING PARTS - IT SIMPLY REDIRECTS THE FLOW OF FLUID ... HE WAS ABSOLUTELY SURE IT COULD NOT POSSIBLY BE THE ISSUE .. I DON'T KNOW THE ANSWER BUT THEY ALL DO IT ! M640 ... BUT AS I SAID BEFORE, I'VE HAD NO PROBLEM, AND SINCE I STOPPED LISTENING, I DON'T EVEN HEAR IT !!!