I have a John deere GT225 with a 16hp kohler. Its been a great tractor so far, but lately when I start it up it smokes white for about a minute. Its also been making a slight tapping sound. I check the oil all the time and its been clean, but last weekend it was low on oil. do you think it is burning oil due to bad rings in the piston or something else? How much do you think it will cost to repair?