I have the 601 as well. When I turn the volume knob to max there is absolutely no noise at all, so you definitely should look into that. You may have a bad unit, but more likely it's due to dirty connections or electrical interference. Make sure there aren't any power cables or surge protectors near the speaker lines.
As for having to turn it up high to get satisfying listening levels, that's not unusual on decent equipment. You'll find with lower-level receivers and boom boxes, there's a big increase in sound between 0 and about 50%. From 50% to max, it's not a huge difference in volume. It's a marketing ploy to make you think you have more powerful equipment than you really do. ("Gee, if it's this loud at only half-volume, this sucker must really rock!!!"). With better equipment, what you want is sensitivity. Yeah, during the day, I have to turn my Onkyo up to about 75% volume to get it where I want it. But at night, when my wife goes to bed, I can have it at 25% and still hear every detail and nuance. It's just a little quiter is all. And no way would I ever actually turn it up to max and run a signal through it! Ear drums, speakers, house foundation, neighbor's house foundation--they would all take a pretty nice beating.
Basically, don't worry about the volume level. As long as it can get loud enough for you, that's all that matters. The Onkyo 601 is one of the most reputable receivers in its price range.
