Sounds like a bad connection b/w the capsule and preamp. However, if it's happened with both pairs, could be user error. Make sure you're installing it right. Maybe take them down to the shop where you got them and ask for help. It's budget gear, but the products should work.

mine are solid as rocks. even droped one from 7' high and it took it with no problem. though i do not sujest this.

Hi
Check the voltage of the phantom supply on your mic preamps....I found that my Davisound preamps don't have enough snot to power my Soundelux U 195. Lovely preamps but weak phantom.
Put a meter across pins 1&3 and 1&2 and check the dc voltage. Two bad pairs is unlikley.
cheers
Roly

What's the weather like there right now? Sometimes this can be cause by extreme humidity. It's possible that if you leave the mics powered up for a long time the problem will temporarily disappear. This isn't super common but it does happen. There was a recent thread about humidity and it's effect on recording equipment so you might do a search. Good Luck!

I have had that problem with modular mics (AKG C451s, mainly) and that was caused by excessive humidity here in Florida. Have you tried just leaving the mics powered up for a period of time to see if they stabilize? Mine would usually stop "spitting at me" after 30-45 minutes. I have heard that a very carefully-applied bit of Caig Deoxit Gold to the contact point will help eliminate this, but the mics were stolen before I could try it.....I was told that that was a problem common to mics that used a certain FET design.