My 92 Ford Explorer knocks a bit when I switch gears.
Check your u-joints. Park the Explorer with the emergency brake on, leaving it in neutral (flat ground, please). Crawl under your vehicle and grab the drive shaft and turn it to see if there is any movement difference or makes any noise. Also, push it in different directions (up/dow) to see if there is movement or noise. If there is a problem there, you should be able to detect movement.
When I shut off the car, I can hear a bit of bubbling coming from the coolant/wiper fluid reservoir.
These are two very different places on your vehicle. One (the wiper fluid reservoir) will not have anything happening to it as described (no way for this to happen). Which leaves us at the coolant overflow reservoir.
Have you actually witnessed it happening, or are you just hearing noise and assuming that's what you are hearing? If you are assuming, I'd state what you are hearing is more than likely the gurgling noise of an AC unit, which would be perfectly normal.
If you have actually witnessed the overflow gurgling, you may have weak radiator cap which is not holding the pressure like it should.