The classic cabinet doesn't have a lot of low end. When cranking the LF up, you are trying to compensate for that by blasting the cab with LF. That uses up a lot of power on the LF and can end up with you clipping early and yet not having much if any more total volume.
Then if you have an active bass, and crank up the gain, you are hitting the preamp with lots more signal, trying to compensate for the power lost to blasting the cab with mostly inaudible LF that won't come out of that cabinet.
The fart sound is probably clipping of the low end. it isn't a 'characteristic sound" of any amp, but more a characteristic sound of trying to get LF that isn't going to show up.
I notice that you have ALL the EQ up. All at 2 or 3 o'clock. AND the gain up. Sounds like you are trying everything in an effort to get more volume out and keep the lows.
Frankly, you may simply NOT be an SVT customer.....not everyone is. You may be lots more satisfied with an SS amp in the 1200 watt or larger range.
Try a preamp and separate large power amp........ but NOT with the classic 8-10. If you want an 8-10 get one with a higher power rating, since the speakers in the classic 810 will hit the magnets and make a sound like a pistol shot with 1200+watts.
If you don't think you would like a bigger SS amp, try reducing the LF some. Maybe try letting the EQ be flat, and then working from there. To get the volume from the SVT, you will get some "thickening" of the sound due to power amp clipping at the mids and highs. But if you let it clip at lows, you probably won't like it.
The SVT is "pre-mixed" to 'sit in the mix" between the kick and the guitars..... "just below a Marshall amp".
Most troubles seem to come from people trying to move it out of that "mix slot" and get it lower into the kick range.