I used to suffer with similar static noises and occasional louder noise bursts when i used G2 wireless systems.
I moved over shure but as I'm considering a change of my mics I had hoped the G3 and 4 would be better.
Does the G4 have better reliability and fewer issues or is it a likely to be the same story if it's a small upgrade from the old technology.
That depends on what you're looking for (application, number of systems, etc.) and why you were having problems with the G2s. I generally consider Sennheiser G2 to be a very reliable wireless system (especially for their price) when properly setup, coordinated, and maintained.
From a reliability standpoint, the biggest change I can think of that started with G3 is that the beltpacks have a slightly different connector mounting (they don't tend to spin around when not locked in properly, which would eventually lead to failure in the G2 packs). I'm also under the impression that the G3 RX front ends have better selectivity than the G2s, but I've never tested that myself.
-Russ