Help, car stereo being weird
 

Hey so i went about installing a cheaper off brand stereo into my subaru, and all went well. Powered everything great for months. Then the time came along that someone stole the stereo out of my 1996 explorer, and so i went about installing the same radio from amazon into my system, bypassing the stock amp and re running wires to individual speakers. I put it all in to find out after troubleshooting that it was a faulty stereo i had purchased. So then i grab the one out of my subaru to make sure i was right and sure enough it worked fine and powered the door speakers nicely. So i take it for a drive to autozone, and as soon as i hit a bump in the road it quit working. Now it wont even work in my subaru. What could possibly have happened?