Distortion Appearing in Different Amplifier Channels? Help Me!!

I recently installed an amp and two subs I was lucky enough to get from someone I found local here on the forums. This is my first amplifier install. The first problem I had was distortion in the left front speaker (not sure what kind of distortion, sounding janky at higher tones usually). I play a song with higher tones to hear it. It shouldn't be the settings messing it up because the other 5.25" is fine. I opened the door and inspected, and realized there was water inside that had gotten on the speaker and the wire. I replaced the speakers with identical new ones and sealed the vapor barrier (that's why water got inside). Problem still there. I ran wire directly to the speaker in the door (14 gauge) to the amplifier. Problem still present. I eliminated that channel (ch 1), and ran the fronts on 3+4, rears were on ch 2, nothing on ch 1. I did test different wire on ch 1 and different speaker, anything on that channel went distorted. I then started having distortion on ch 3. (left front again) That speaker worked fine on ch 4, and ch 3 was putting out the distortion. I switched my L and R on the amp from the RCA's and it was still on ch 3. I don't think RCA is a problem anyway because it isn't on the 6x9 on the same side (only one set of RCA's). I have yet to check if ch 1 is working (got better with time maybe?) Other than that I have some headlight dim on sub hits, and have had speakers (subs especially) cut out at very high volume with high bass, but only sometimes. Power delivery is a question, but my ground is good, and I've checked the power wire. Other than buying a bigger power wire I don't know what to check. If it was a power issue it would be all channels anyway wouldn't it? Other possibility... The power wire is going through the door jamb and it did get slightly pinched, but the wire inside the insulation doesn't seem affected at all. Since then I secured it away from all moving parts, no more pinching. Not sure about the gauge on the power wire since I'm new and can't eyeball it, but it is what I was given with the amp and subs, and this man definitely knows what he's talking about so I doubt he gave me something too small. He will come help me out when he has time, and I do appreciate that. I just want to get ideas of what I could troubleshoot in the mean time by myself, save him the time possibly!