Plugged them into my pc and the volume is all the way up and it's not loud at all. However, I use my stereo speakers and the stereo itself when im not using a headphone. I connect the stereo to my pc through an auxiliary cable. I just plugged the headphones into the stereo headphone jack and the sound is much louder. However, there is a humming noise. Is this bad? Should I just get an amp?