Unhappy [Q] G2 weird signal issue on T-Mobile (video)

I've experienced an issue with the signal constantly dropping and gaining when using a gsm sim card.
Restarting the phone doesn't help. triggering airplane mode doesn't help either.
First time i put t-mobile sim card in, it works for a few hours and this happens since then. sometimes i try putting in my friends' sim cards in and it works for a few minutes.might this be a software problem?

this is a short video of the issue in case you can't imagine what I'm talking about youtu.be/nOw3jZyiNBA