My van has been making a sound I can only describe as the sound of ice breaking apart-a rattling of sorts I guess in front of dash towards the hood. We have a leak of antifreeze but mechanic has not been able to ascertain from where it is we are losing it. The van has been running well. Today was very cold, about 2 degrees with wind chill of -15. We started and ran in driveway for about 15 mins and it sounded fine but once I started driving that “crackling/ice breaking ” noise was very prominent then when trying to accelerate the whole van was rumbling/shaking. Any thoughts?