Amps chasis is grounded?

I recently installed a alpine 4 channel amp and had a problem with it cutting out, so check all the connections and found out that the 8 guage ground wire might have a bad connection because I did not sand the paint down. I disconnected the ground wire, then I had to move my car and when I started it the amp turned on with NO GROUND ATTACHED! I was like WTF! and found out that the amps chasis is being grounded to my seat back!

Is this normal, because my other amp doesn't do this.

Any body have any ideas why its cutting out, probably related.

If your other amp does not have as conductive a ground plane as the first amp then no, do not expect this to work. Yes it is normal for some amps to do this, it is also one of the sources to consider when you have a ground loop. The ground wire is the most important wire in your system, make sure you have a good solid clean ground with as low a resistance as possible.Top Secret, I can tell you but then my wife will kill me.