help please not sure whats wrong

[jake1993]

i pulled my friends kenwoods (single 4 ohms and i had 3 of them)out the other day that he let me play with to see how they sounded in my truck. the amp was working fine before i pulled them out. then i decided to try to build a 4th order and try my little 10 out. i put it in the truck hooked the speakerwire up. (this was like a matter of minutes after i pulled the kenwoods out)turned the car on to see how it sounded and when the amp turned on the sub just played a loud buz. so i tuened it off check all my wires everything looked fine. i pulled the amp out brought it in and hooked it up on a car battery and charger in the house. hooked the same sub that was in the car up on it and it worked fine. so i took it back out and hooked it up and it made the same noise as it was when i pulled it out. im thinking maybe the headunit might be messed up.what do you guys think? gonna hook it up in a friends car tomorrow to test it again. but looking for any ideas why its doing this. its under warranty but i dont wanna send it in for them to tell me its fine and nothings wrong

[Guest]

i'd check the rca's first to make sure a wire didnt accidentally get pinched somewhere.

[jake1993]

i did. i pulled the headunit out and used a different pair i know was good and it didnt affect it any