Help: Tube Amps Pops Speaker Cone

One of my single-ended triode monoblocks makes a loud popping sound in my speaker shortly after turning it on. There is an LED on the amp to indicate the proper waiting time for the internal tension of the amp to be adequate for functioning. After this LED goes on (to indicate it is ready) the amp then initiates a sequence of pops of decreasing volume in the speaker for a few minutes. There is also a hum present that largely disappears when music is played over the speakers. What is the problem with my amp? What can I do to stop this popping? I am afraid of damaging my speakers.