Volume increases or dies completely all of a sudden

[mambo]

Hello all! I have a Marantz SR 6009 9.2 channel receiver and I primarily use it in my 5.1 channel home theater system. Of late, it has been acting up. After an hour or so, the volume seems to increase to the highest levels causing very loud sounds. Sometimes, the volume is completely gone and when I turn the volume up or down, it is back. Before the volume dies, distorted, crackling noises are heard through the speakers for a brief moment. The volume level that's displayed seems to not change.

It has happened a few times and I will be taking this unit to a service centre, but wanted to see if any of you have experienced a similar issue and if you can give me some advice.

Thanks and regards!