Replying to Need Some Help With My Car Sub

I had a 300W Polk Audio amp and 10" Kicker sub installed in my car a couple of weeks ago. The sub works fine when the car is off and I just have the radio on. But sometimes when I start driving, the sub won't work at all...Every now and then it will turn on and off, but then once I've been driving for awhile, it will work fine. So basically when I get in my car in the morning and start driving, my amp won't be working. Then when I'm at a stop light and just idling, the sub will come back on but turn off again once I begin driving again. Anyone know what is going on here? If the amp is cold, could that cause it to not work? Or could it be something with my battery? I checked for loose connections but didn't really see anything that was loose.