maureenzakrzewski , You may need a new volume switch/ amplifier rotary encoder, I would try cleaning the switch before replacing, as it seems a lot of people have success after cleaning. See below links #1 and 2 to volume button cleaning how to and #3 and 4 possible places to purchase a replacement control if needed. Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.

https://www.youtube.com/watch?v=y4XF9Poi...

https://www.youtube.com/watch?v=VjKcPU2k...

http://us.marantz.com/us/support/pages/o...

http://www.oaktreevintage.com/index.htm