1996 Ford Explorer Shaking btwn 35 and 50 mph

About a month ago, my dad replaced the wheel bearings, upper and lower ball joints, spark plugs (but not harness), and the air filter. Everything was good, and I put a couple thousand miles on the SUV.
Today, hundreds of miles from home, the truck started making a sporadic, non-constant staccato popping noise, much like a bottle rocket going off. I was unable to tell where it was coming from, as it only happened while I was driving and stopped when I was in park. It did not recur when I revved the engine in park. After about 15 mins, it stopped. A couple hours later, I was driving and noticed that the car hasda bit of a shake felt thru the steering wheel from about 35-50 mph. I did not have a chance to go much faster, so I am unsure if the shaking would return at 60 mph. I detached the spark plug wires one by one, but did not find one that was obviously bad. Any ideas?

Part Two - The STUPID driver's side door lock will NOT unliock with the keyless entry OR with the key. The only way I have found to open the door is by reaching around from the back driver's side door. THIS WILL DRIVE ME CRAZY. It also does not lock, although I can push it down to lock it. The lock/unlock switch inside on the driver's side locks all the other doors, but does not do anything when I push unlock. Any ideas on this?