Could you describe this noise for me and if it is short or long? If you are concerned, you could always try recording it (perhaps with a phone) and then uploading it onto here so that I can take a look (or should I say ..... listen).
After turning off the camera, it automatically performs sensor cleaning. This is accomplished by sensor vibration and some models additionally feature ultra sonic waves to remove dust from the low pass filter. This causes the noise and the high frequency sound.