Audio Speakers Really Quiet?

I have put a stereo on the front of my motorcycle. The other day everything was fine with them. Today I can barely hear any sound and the sound keeps cutting in and out. I dont have an antenna hooked up but when I switch to the radio I can the static just fine. Its when I try to use a Aux cable, SD card, or usb that I can barely hear anything. I switched to the static and tested all 4 speakers and they all work. Anyone know what it may be. I am not using an amp. Its a dual head unit with 4 polk speakers. Wire speakers are hooked up. Then I got the ground grounded, power to the battery, and a trigger wire tapped into my rear light so that the radio only comes on when I turn the key on. Thanks