You NEED to check it with it running. From my experience, air bubbles often occur when the level is too low, not too high, unlike engine oil. If you can't get a solid reading on the dipstick, it's USUALLY because you're a cup to a pint low. if you pull it out and the bubbles are on the tip of the dipstick, the fluid is low and foaming and the foam is what's touching the dipstick and dipstick tube.