Hey, today i decided to install another amp and another sub that i had lyring around, when i took them out of my old car they worked fine. I ran both subs in mono on each amp. now im getting a loude humming sound coming out of the old amp when i run it to eather sub, it doesnt do this in my old car, i even set it up in my old car sence i still have the harness in it. To rur both amps, a four gage wire is coming off the battery, and about a foot of 12 gage wire going off of it to the amps. i have the same set up to the ground. When i run just the new amp i get a small hum, but its not nearly a loude as the old amp. Im pretty confused at what it is, but i have a fealing it is the right input wire off of the deck. any ideas of what to check?

Thank you mobil one for rust proofing my driveway.