Tracking down a hum.

Mine is a line stage. Look for a small orange and white switch it's upright and small, near the transformer.
I was able to find it without too much trouble

Well after the weekend the noise is back. It's through the speakers and independent of the volume control. It goes back to Rogue this week with my contact information and a description of the problem.

Sending it to Rogue. I'll post here what they tell me the issue is.

@noromance and others. I got a call from Rogue today. It's repaired. They replaced 6 components. A bunch of capacitors in the power supply and a resistor in the voltage regulator. Cost $255.00 all told. Disaster has been averted no explosions.

@noroamnce, kudos. I'll know more about which caps were replaced when I see the invoice on delivery.
@thecarpathian. The explanation given to me is they were unable to get schematics with values and were reluctant to work on it as such. Rogue would not provide them either.

Okay I got the amp back today. I was hoping for an itemized list of parts replaced. I didn't get one. It looks like the replaced all the capacitors in the board nearest the transformer, and one resistor was replaced. I'm listening now and so far so good.

Well after listening for a couple of hours out of nowhere the noise is back.Evidently the folks at Rogue missed something. This time the noise doesn't dissipate. The noise pulses. get louder then softer louder then softer. I have no idea what the cause is now. I'm thinking a faulty rectifier.
This is frustrating and starting to get expensive.

@ jond I don't think its the line. I swapped out the amp with an old NAD C 340 using the preamp outputs and everything is fine, nice and quiet. No noise in any other components using the same outlet.

Oh yeah I sent it back to Rogue this morning. Power supply and all. There isn’t much in the external power supply, a transformer, some wires and a fuse. I don’t remember much else.
Hum is present in both channels and pulses. Failing rectifier maybe?
People are trying to tell me its an issue with my power outlet or a compatibility issue with my power amp. I’m starting to think it’s a ground loop issue. I know it’s not my power amp or my local utility that’s causing the problem.
We’ll find out soon enough. I’m about ready to call in a Priest to do an exorcism!

A bad solder joint would not surprise me. I bought this thing used and it had a bad solder joint in the left channel variable output. Got that fixed no problem.Hopefully they'll get it fixed. If they don't I'm going back to a solid state integrated amp.

Well today I swapped emails with the people at Rogue. They found a faulty SW 5 switch. This is in addition to replacing 5 capacitors earlier. I need to get a new battery for my multi meter, and a set of precision screwdrivers so I can get at the battery. This in order to check the voltage coming from the outlets. I should have it back early next week.Wednesday most likely.

Well I plugged everything into a different outlet. So far so good. I'll have to give it some time to see if that really was the problem. As whart said. "It's usually something stupid."   It appears jond was right as well.

Story has a happy ending. Since the source of the hum has been found and dealt with It was the power outlet I was using odd in that it didn't affect anything else in the system Combined with the new parts installed by Rogue. This almost 20 year old Model 99 sounds AMAZING! Got the best of both worlds right now.
 

Thanks for the repsonses. I think boomerbillone is on the right track.

Thanks for the responses. I swapped tubes out and powered up the system, same result. Looking at the capacitors, they all LOOKED okay (no bulges or anything). Their are no capacitors in the external power supply so it's something under the hood. Either tube heaters or a bad capacitor somewhere. Fortunately this should not be a prohibitively expensive fix. It goes to the shop tomorrow.

@imhififan  I have swapped out tubes, the condition still persists. I connected my headphone amp to the power (briefly) no hum coming through that I could hear. So I think it's in an output capacitor or in the tubes heaters. It isn't the tubes themselves. 
Thanks for the advice.

Post Script to all this.
I took the amp to a shop for repairs. The techs (2 of them both experienced) could not find an issue. Told me everything in the amp is "up to spec". Gave it back to me no charge. Get it home hook it up and the hum is still there. Only now it is constant. I call Rogue. They say try the dip switch in the voltage regulator. I found it and switched it from H to L and now everything is fine. Hum is gone amp runs nice and quiet. If it happens again. I'll send it off to Rogue.
Thanks again to everyone for your input.