I'll defer to the more experienced crew here on the door thing but my only comment would be - disconnect the battery for 5 minutes (if you didn't have it disconnected when you disconnected the door wiring - and you should have!).
Regarding the whine - sounds like interference from something, probably due to the earth connection you have used. For an installation like this, you want a REALLY good earth on the main amplifier, and preferably the same good earth point as the H/U. Hard to do in your case but if you have the main amp. in the rear, then connect the amps earth to the negative battery terminal. Then connect the H/U earth to the large earth terminal under the bonnet (hood) on the left side. You can make these temporary connections (with BIG wire!), then test your sound system again. If the whine is gone, you know what to do...
