Can TV cards and cheap STB's be quite fickle when it comes to bad signal?

The reason i ask this is as follows.

I have 3 DVB-S devices connected to a splitter.  From time to time my TV card gets really bad picture quality (lots of break ups etc).  This is often resolved by re-screwing everything into the splitter.  The thing is that nothing is every very loose, but still, this process seems to fix it.

Odd?