DC-2 hiss / white noise

I recently got this Mesa DC-2 (studio caliber) in for a repair. I've been through a lot of Mesas the last few years and I really love them when they work, but they are usually a real bi*$& to work at. So - I thought this one only had bad tubes, it had a lot of white noise and crackling and popping going on. So I ordered new tubes and installed. The crackling and popping went away but there is still way too much hiss going on. There is actually more hiss in the clean channel than in the lead channel. I have rolled tubes and put in tubes that I know work well in other amps, but no luck, of course there is a tiny difference between different tubes but only slight, as you'd expect. I have also tried to reflow the tube socket pads.

I have linked to a DropBox-folder with a sound clip and the schematic (the DC-3 has the same pre-amp) In the clip I first turn the master up, then the channel master and finally the gain and then fiddling a bit between about 7-10 which cause a bit of scratching. Reverb is off, the other controls is at 5. Then I switch to the lead channel and repeat. The scratching is not as present in this channel I think, and hiss is also more "normal" here, though I think it is a bit too much. Finally I switch back to the clean channel... the hiss is louder.

I used to own a DC-3 some years back and that one did not have this excessive hiss. I think the only difference between DC-2 and 3 is that the DC3 has the graphic EQ and it sports 4xEL84. The DC2 has 2xEL84 and has a fixed set of inductors to "simulate" the V-shape on the parametric EQ (called Contour).

Is there anyone who got a clue where to start? Chopsticking make the usual high pf ceramic capacitors pop, but that is fairly normal, right? Other than that there is nothing sticking out. The 1meg resistor right before V1A pop also, but I've tried to solder that one out without any change. The owner have modified the circuit to have a serial FX-loop instead of a parallel, I haven't closely inspected that part but it seems okay at a glance, but coud there be something there?


https://www.dropbox.com/sh/6sjkgbihlsbqnpn/AABXtJx5aT3FgC78VSNGr0Jna?dl=0

I forgot to mention that I also tried to pull tubes. If we look at the signal chain for the clean channel it uses V1a before gain, then V4b and V4a before channel master, then into V3b and finally into V6a/b for PI. Pulling V6 remove all hiss. Pulling V3 remove all hiss. Pulling V4 remove almost all hiss, and pulling V1 remove a lot of hiss, so it seems like might be building up along the path. Pulling tubes has about the same effect as turning the gain, channel master and main master in the sound clip.