ok.. i have installed my system.. stock HU with a hi/low convertor.. and the amp with the sub.. 2 problems.. my sub when i turn on my car and off makes a thud.. i think it's the amp.. the amp is a crossfire tek 50.2.. also whenever i turn OFF my head unit.. i get major distortion feedback from the sub.. kinda like the sound when the THX thing gets super super loud.. so basically to correct that im driving wit da radio on min volume.. so wut's the problem? i thought it was amp groud to sub.. but when i took out the RCA's from the pre-amp.. i didnt get feedback noise when i turn off my head unit.. so im guessing it's something with my hi/low.. i think it might be the grounding point i picked for my high low.. or my antenna.. i dunno.. i guess i need help. thanks..