I have a problem with my subs cutting in and out. They always play but are hardly ever at full power. I will be driving and then they will kick in and it seems like when that happens they are receiving a lot more power. I currently have my amp grounded on the sheet metal trunk floor. I sanded and scraped away all the paint, there is nothing underneath the metal except another layer of sheet metal(so 2 layers total). I have checked all other connections and had my friend check them too, they seem fine to both of us. When it gets warmer I am going to drill a hole and ground it straight to the frame or chassis.
My current and only amplifier is a Hifonics BXI1206d. I used a 4awg amp kit from knukonceptz for my wiring.
My previous amp was some crappy 150w wal mart amp and it worked fine, but i suspect that was because there was such little current compared to my current one. I am running it at 1 ohm, and set it with a DMM to about 850wrms.