tuner hum ???

I have noticed that when my tuner is off but I have the preamp set to the tuner input that when I turn up the volume I start to get a hum when increasing volume of tuner input when the tuner is off. I do not have this issue with my CDP which has no hum even when CDP is off but on CDP input with increased loudness. Is this a normal phenomenon with tuners or should I get my Magnum Dynalab Etude looked at. I think I may have noticed this same issue with my Jungson tuner in my Jungson system. Do Tuners hum when off but input has juice put through it?
I actually don't have this problem with my Jungson tuner. This makes me wonder if their is a problem with my magnum dynalab??
Sounds like it may be a ground issue. I had a very similar problem just recently.

Try floating the ground on the tuner.
With signal of station hum dissappears. The hum is not just masked but dissappears. I checked this out carefully.
It's as if it has to do with the mute function but that is ok as I listen to clear received fm which has no hum. Any ideas why?