[Music in a bottle]

Let me ask you guys this. What would cause a mechanical thump in an audio component upon power up. Sometimes it makes the thump and other times it does not . Sounds like something hitting the cabinet pretty hard. My father could hear it over the phone, and he's partially deaf! I just have it setting now in the off position, afraid of doing severe damage. Have 3 complete parts rigs in house. It is over 40 years old but solid state and fairly obsolete looking inside by appearance. Any ideas? httpphotobucket.com100_0509.jpg