Yes. Even if the input is digital, you can still have too much gain and that could generate some noise.
I just thought of something else. Try unplugging your sub. Do every thing; power cord, IC's.. Anything that goes to the sub.
"But i couldn't help but doubt that the NAD weighing just 4-5 pounds and can really drive my Excite 12 speakers."
That's nothing to worry about. The reason its so light is because its a class D amp. They don't generate a lot of heat like a traditional amp. Class D amps don't need big heat sinks and other parts that weigh a lot. Even expensive, high output class D amps weigh very little.
I just thought of something else. Try unplugging your sub. Do every thing; power cord, IC's.. Anything that goes to the sub.
"But i couldn't help but doubt that the NAD weighing just 4-5 pounds and can really drive my Excite 12 speakers."
That's nothing to worry about. The reason its so light is because its a class D amp. They don't generate a lot of heat like a traditional amp. Class D amps don't need big heat sinks and other parts that weigh a lot. Even expensive, high output class D amps weigh very little.