Help me trace this noise(s)

[Morocotopo]

Hi, I wonder if you could help me trace this noise in my build. It´s a LHX2 fender amp and cab simulator. All opamp based. It works good, fully functional, but i get this noise every 20-25 minutes approximately (file maximised for better hearing):
http://www.aronnelson.com/gallery/main.php/v/Morocotopo/LHX2++whine.mp3.html
From what i can tell it´s an oscillation. I redid all wiring to get it as short as possible (moving wires around doesn´t have any effect on the noise), sensitive wiring shielded, placed caps (104) at the power rails of each opamp (it´s a +/-9V circuit), tried a 100R in series plus cap to ground in the power lines, tried a 220V power line EMI filter (little thing with some inductors and caps inside)...
Don´t know what else to check. The only thing remaining to check (at least that I can think of) is that the same dual opamp (same physical package) is used in the layout for the very first opamp in the schem and the very last one. Could that be the problem, I mean, internal oscillation in the opamp, because of the schem´s gain? I believe that this opamp (TL072) has around 100 dB of crosstalk attenuation. Is that enough?
Any suggestions?

And also, the cab sim also works good, but it´s quite hissy. Can´t get the output over a quarter of the way up cause the hiss starts to be intrusive
Schem:
http://www.aronnelson.com/gallery/main.php/v/Morocotopo/LHX2-FENDER-CAB-SIM-SCHEM-N.jpg.html
Do you think it´s because of the 13 (!) opamps used (I mean unavoidable, -->accumulated hiss), or can you spot any problems with the design?

Thanks for reading

Morocotopo

[Paul Perry (Frostwave)]

It sounds more like interference from the mains, to me. Even though you have a filter.
Can you try it on batteries?

[Morocotopo]

Thanks Paul, actually, I tried it with batteries when I fired it for the very first time, long time ago, but I don´t remember how it worked... will try, good idea, so that I can discard/point at the power supply as the source of the problem. By the way, the PS is mounted inside the same box, bipolar PS with 7809 / 7909 regulators and all usual caps, internal transformer, mounted in a "sub box" inside for shielding. I don´t get any 50/60 Hz hum.

IF the problem is mains interference, what would you suggest to get rid of it? I have it plugged into the same power circuit as my mixer, computer, cd player and assorted apparatus in my studio. I have line power stabilizers for the computer, etc. Could that be a factor?

Thanks

Morocotopo