Car Stereos: pioneer 3000ib, wiring connections, gf

Question
i have a pioneer 3000ib that i bought new. Now when i try to hook a amp up for my sub or 6x9s it puts out like a screeching noise or just a pulsating sub. I no is not my amp or wires because my gf has the same radio and i just plugged the wires in and it worked great with her radio in my car. so i tried putting my radio in her car and the same noise came out. every thing else about the radio works great. what could it be?

Answer
Ricky, just trade your girlfriend radios and be done with it.  Seriously, your problem is a little tough.  I would double check all wiring connections and be sure they are right and tight.  After making sure they are good, the only other fixable problem is the radio settings.  Check all the settings in the radio for the sub outputs.  If the settings are all good and connections are good, I would think there is something wrong with the unit itself.  You have done well in researching the problem yourself, so hopefully one of these solutions will solve the problem.  Good Luck, Scott