Ah, the dreaded "noise floor". I HATE having any sort of noise floor. I chase silence from my sound system in exactly the same way I chase a true black from my display
To answer your first question: hiss is very common, but it should NOT be audible. Many, many, many amps will produce a very low-level hiss, regardless of anything else that may be happening in your system. But it should NOT be audible. Sometimes, you can put your ear right up against the tweeter of your speaker when nothing is playing and hear this low-level hiss, but at your seat, with nothing playing, it should be dead silence. That's the goal, anyway.
If you can hear a hiss while you are watching a TV show, then that is NOT normal. A lot of components produce their own hiss or buzz. It usually comes from the power supply. Subwoofers, amps, receivers, TVs - they all might produce an audible buzz or hiss. My Pioneer Kuro KRP plasma monitor produces a buzz from the plasma panel itself - it is my ONE complaint about this otherwise nearly perfect display!
But an audible hiss from your speakers while you are watching a TV show indicates that something is not right. With that knowledge, it's a matter of tracking down the source of the hiss.
Try disconnecting everything except your speakers from the receiver. In other words, zero cords attached to the back of your Onkyo except for the speaker wires running to your speakers. Turn on your receiver and see if you have an audible hiss. Try going to all of the different inputs (DVD, Cable Box, Tape, Phono, Aux, etc.) See if all of them produce a hiss or just some of them or none of them.
If you do not hear any hiss from any input selection, then we know that the hiss is not just coming from the receiver itself. If you DO hear a hiss, it isn't necessarily the end of the world. If you hear a hiss from some input selections, but not others, then that indicates some sort of circuit problem in your receiver and you should have it serviced or replaced. The hiss should either be present with all inputs or none of them when there is nothing but the speakers attached.
If you get a hiss regardless of the input, then try connecting just a stereo RCA L/R analogue device (eg. a CD player) to an input. Select that input on the receiver, make sure it is set to use the analogue input (you can usually choose if you want to use the analogue RCA input or the optical, coax or an HDMI as the audio source). Turn on the CD player (or other analogue source), but do not play anything. Did the hiss disappear?
It's actually pretty normal for a receiver to produce a hiss from the speakers when there is nothing at all attached, but then go silent as soon as a source device is connected and powered on. If this is what happens, then we know that the problem lies either with the specific input that you are using for your Dish box, or the hiss is coming from the Dish box itself.
So, naturally, try connecting that CD player that you just used to test the receiver to the input that you would normally use for your Dish box. Try the analogue RCA L/R connections, try the coax connection, try the optical connection. Set the receiver to "look" for the input that you are using and see what happens with the hiss. If you can get the input to work without a hiss, then we know that the hiss is coming from the Dish box itself.
Hope that helps!
