whenever i plug my 404 into my computers mic jack from the line out on the 404 i have this constant feedback sound

also whenever i plug my headphones into the sp its a lot more quiet and reasonable unlike whenever i am listening to playback through the computer

any tips or is this just the sp messing up

could be a ground loop issue. Try different configurations of plugging your gear into the wall and see if you can fix it..

also, if its grounding, try to unplug your computer and use your laptop battery when recordin g your 404.

or connect a ground wire from your 404 ground screw, to something else live, like the speakers or ?laptop if you kan.

You def have a ground loop which are a major PIA but also laptops are worse because they introduce noises from hard drives and other components. If unplugging the laptop mostly solves it you have a ground loop.

I bought one of these recently- problem solved-
http://www.amazon.com/gp/product/B000LP ... UTF8&psc=1

Also these can help-
http://www.amazon.com/Ebtech-Hum-Voltag ... ords=hum+x

Good luck- and let us know how you get on.
C