Component grounding

No no, I meant the preamp section of the integrated. It has a feature that let's you bypass the preamp section and use the output control on the DAC instead. When I did this, the hum came back. I don't know what that means, but you're right, the issue must reside with this particular amp because I've never had a hum otherwise. 

 

That sounds like a problem with the DAC. So if the amplifier is using its internal preamp, no hum, but if you connect the DAC to one of the inputs and use the preamp section's volume control- you have a hum (or buzz), right?

If yes it suggests an issue with the DAC. Since you did something to it as suggested in the posts above, it might be that there's more to it than a missing shoulder washer.

@atmasphere -- That's starting to seem to me like a likely explanation also. Plus the fact that the hum begins when the interconnects are inserted, not when everything is simply powered on. But I really didn't do anything to the DAC except switch the fuse. I'm very careful when doing any kind of operation with my equipment, and as I said earlier, there is no hum with the other two integrateds. One is a solid state, the other a tube.

I installed the nylon washer between the chassis and the ground wire ring. Then a ground washer screws against the ring. Is it worth trying another nylong washer between the ring and the ground washer? 

I installed the nylon washer between the chassis and the ground wire ring.

That doesn't sound right! If there is a connection to the chassis (and I'm assuming it comes from the center pin of the IEC connector) it would not be insulated from the chassis by a nylon washer!

Am I misunderstanding?

I wish I could post a photo of what I mean. If you follow this link to page 7, it talks about a ground wire running from a grounding block on the floor of the chassis to a screw on the side of the top cover. Before you can do anything internally, you have to disconnect this wire from cover; otherwise you can't get the cover out of your way. So, what I did, I put a nylon washer between this wire (which has a ring termination) and the chassis. Then a ground washer goes onto the end to screw it all down. Does that make sense? 

OK, I can't post the link. Anyway, it doesn't say more than I just said.