Hello, our well-used Rode NT2 condenser mic has developed a problem. When miking at low-levels it's fine in every way. But when we use it for vocals or high-pressure stuff it only works for a couple of minutes. Then the audio fades over a few seconds to be replaced with a fading-in loud hiss. If we allow it to sit without any audio for a few seconds it recovers again. It doesnt matter what pattern we have selected (omni/cardioid) or what output level is selected. I have replaced all the semi's on the pcbs (2 audio preamp transistors, the oscillator and fet) with new ones (they're only pennies) but it hasn't cured it. I've gently baked the capsule over the weekend in a warm closet that's shared with the boiler, this seemed to make it work for a good 10 minutes afterwards but now it's back to its old tricks. Any suggestions ppl?