ok so I got everything wired in how I would on any other car, and all I get out of the speakers is a hiss. I can hear the sub turning on and off with the car, but no sound. Is there any kind of modulator or anything that these cars need to use an aftermarket HU?

I just bought an 05 vibe gt with the monsoon sound system. The previous owner had installed a double din pioneer headunit and focal front speakers running off of a jl amp. He also had a 10" rock fosgate sub with an alpine amp which just takes up too much damn room in the trunk. I'm not currentl...