I changed the pots out of my MIM stratocaster and put in USA pots.
Now I have a static sound when I play. Could this be a cold solder
joint? Should I put foil tape in the control cavity and on the pickguard?
The tone is a lot nicer but I cannot stand the "static" sound that comes
thru.
I hope someone can help me with my problem as my son bought it
for me for fathers day.

You have a loose connection somewhere. Forget the foil tape business as it has no relevance to your problem. Open up the guitar (obviously) and inspect point to point the soldering of all your connections. Pay special attention to your volume pot, output jack and pickup selector switch. If you cannot resolve it, post some pictures and we'll try to get to the bottom of it.

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You dig?

While it could be a bad joint (you can just add a bit more solder to them if you wanted to refresh them). It might pay to check the resistance of the old pots and compare them to the new pots. You need a multimeter for this.

If you have gone up in resistance in volume pot for example you will have more high frequencies bleed through and if the pickups were noisy to start with it exaggerates the problem.

Since you have spare pots you can also just swap test them. It could be a faulty component you have installed, especially if brought second hand.

Make sure they are all properly grounded to each other and no wiring has come lose anywhere else.

Lastly if you do make modifications copy and keep track of every component so that you can revert it if required.

Let us know what the problem is or how you progress.