About 1,000 miles ago I changed my trans fluid and filter (4l60e) just recently started to here a weird buzz or electronic kind of sound when truck shifts. Sounds like if you were to adjust your power mirrors. It only happens during the actual shift but does it on every gear except N. Sound goes away after about minute or 2 of driving then won't here it again till truck cools off and I start it again. It sounds like it is behind dashboard almost but maybe front of transmission. It shifts completely fine and fluid is right where it is suppost to be, hot and cold. No idiot light or code comes up. Anybody know what it could Be? Thanks.