We have a problem in our apartment with just one of our radiators from which we receive steam heat. Since the heating season began, the radiator in our room has made pinging noises when the heat first comes up. It can last for up to a minute and is just loud enough to awaken us at any hour of the night. We have no control over the radiator since the system is regulated by computer in the basement of our building. Management tells us the noise is metal expanding and it is normal and acceptable. However, this never happened before, and occurs in only one of our radiators, plus we are constantly awakened. Why is this occurring and how can we either stop this pinging noise or muffle it with some acoustical material? Thank you for your help.