The spray cleaner suggestion is not much help without some idea of how to use it. Although there used to be at least one place on the Net which told you how to clean a component, I seem to have lost my link to it.
I imagine the point was that your Marantz probably just needs cleaning, especially its switches and controls. If you get some spray cleaner, open up the unit and place it in a good position to drain, find the openings in those parts, then squirt some stuff in while turning or switching the controls back and forth a few times, that may solve your problem.
You can have a technician do this for you, of course, at the cost of about an hour of labour. He will probably do a better job, but you won't learn as much. Also, if the problem persists after cleaning, a good tech will already be some way towards an idea of the cause.
I imagine the point was that your Marantz probably just needs cleaning, especially its switches and controls. If you get some spray cleaner, open up the unit and place it in a good position to drain, find the openings in those parts, then squirt some stuff in while turning or switching the controls back and forth a few times, that may solve your problem.
You can have a technician do this for you, of course, at the cost of about an hour of labour. He will probably do a better job, but you won't learn as much. Also, if the problem persists after cleaning, a good tech will already be some way towards an idea of the cause.