Yup, I think I will try doing the reseat first and perhaps add a new ground wire, if that doesn't work. I've been searching to see what an appropriate gauge of wire would be for this. Some places suggest thinner wire while some suggest heavier gauge wire. Any tips on this? If I do run a new ground wire, should I disconnect the HU's factory ground wire?
By the way, is it normal for an alternator to make a whining noise when charging a battery that's close to drained? I'm asking because, there were a few times when I would run the car on acc for several hours while doing cleaning, etc. Starting up the car after all that time, I would hear a whining noise that I always assumed was the alternator working harder than usual to recharge the battery. This was when I had the OEM Hifi system. Since I thought it was 'normal' I never really bothered to check if the noise was coming physically from the alternator or whether it was coming from the speakers. Now I'm wondering if that was alternator whine all along...