hT1550 sudden noise problem

[JRUTA]

I have a very well cared for ht1550, that has suddenly started to make a horrible noise upon PTT, the screen goes blank AND NO CONTROLS RESPOND. the only way to "reset" it is by turning it on and off. not a huge deal however the first time it happend, i was with a critical patient, and I REALLY needed the radio- whats worse was not expecting it to fail out of nowhere.

Any ideas on whats causing this? I tried cleaning battery contacts on the radio and battery, I have no changed the codeplug, it has not been exposed to water, not dropped, and I CANNOT forceably make the radio reproduce this failure. THIS HAS ONLY HAPPEND TWICE, BUT IT'S TWO TIMES TOO MANY. this isn't a hobby radio, I need it to work all of the time. thanks.