It's common knowledge among most strat/single coil pickup users that they are more susceptible to noise than humbuckers, due to their similarity to AM loop antennae. Some places may have more noise than others that your pickups can "hear."
There is no hum or buzz at the in-between positions (2 and 4) because having two pickups active helps cancel out the noise, similar to (but not exactly the same as) what a humbucker typically does.
From here, you have two possible solutions for this.
1. Have your guitar's internals shielded with foil tape, as described in this article:
https://www.seymourduncan.com/blog/setups/how-to-shield-a-guitarPros:
* If you like the results, you may not need to change out your pickups
* Aluminum foil tape is available from a lot of hardware stores
* Little to no change in the sound of the guitar
Cons:
* won't get rid of all the noise
* might be a little difficult for inexperienced guitarists to do
2. Buy noise-cancelling single coils, or mini humbuckers that will fit the guitar.
Pros:
* almost no buzzing or humming will be heard, enough for high gain distortion with no noise
* You may like the change in sound...
Cons:
* ...or you may hate it. noiseless stratocaster pickups are known for not sounding single coil-y enough for most purists
A combination of these two methods will give you even more noise reduction. Good luck.