Problem with Counterpoint SA3.1...Hissing/scratchy

I've had this for about 3 years now along with my Dynaco ST-70 with satisfying results. Recently I've been getting scratchy/poppy/hissing sounds that I've narrowed down to the Counterpoint. I've got my Dynaco hooked up to my Outlaw receiver's pre-outs for a temporary solution and no noises are present. When I switch the 6dj8 tubes around in the pre(I'm thinking that if some of the tubes are bad I should still be able to figure out which is good and install that in the phono section BUT... 1)None of the tube sockets are marked as to which stage they drive and 2)Sometimes I get no sound at all after just switching the same type of tubes around) I don't get results. Is this what typically happens when tubes go bad in this pre? What other problems may this be? Should I really shell out $100+ bucks for new tubes or just get something else in the neighborhood of $400-$500? This had some mods done prior to me getting it but I haven't a clue what they are. Any suggestions would be greatly appreciated.
Could be a tube, or, could be the infamous balance control. This series (as well as the 5.1 and 7.1 had really noisy balance controls, manifesting itself in the type of noise you are describing. Try giving the balance control a good cleaning with a spray cleaner. The Counterpoints are really sensitive to microphonics as well.
Does the noise increase with an increase in gain, or is it at the same level regardless of volume setting?
The balance control was completely unwired/bypassed. The noise is pretty much the same either quiet or loud.
I have a 5.1 preamp and popping type sounds were caused by the volume control knob. I spoke to Michael Elloitt regarding this and at his instruction, removed the volume control knob and tightened the nut down.

I later experienced selector switch problems which he repaired.

Bottom line-these are great sounding, but aging units. If you can afford an upgrade/modification of your unit, you will have the great sound and reliability for a long time.

I had my SA20 amplifier upgraded and my 5.1 preamp will undergo the same.

Good luck.

If you get no sound after switching tubes then you definitely have bad tube. Get yourself a new set of tubes.
There should be tube number marking on the circuit board.
My Counterpoint 7.1 had an addendum slip with the user manual that was the tube placement chart, labled v1-v4. The same numbering scheme was place on the pc board next to each tube socket.