I have a 2001 Lexus IS300 and the past two mornings I have noticed within the first five-ten minutes of driving a high pitched whistle. It sounds exactly like a teapot whistling. The temperatures outside have been about 20-30 degrees. I hear the whistle at about 30mph only upon letting off of the gas and the whistle lasts only ten seconds. Today I heard it over my radio/heat which caused a bit of an alarm to me. Any ideas?!