Transformers hum, the magnitude isn't a necessarily a sign of a problem. It could be some part of the enclosure isn't as secure as it should and it's vibrating to answer the sound. Every transformer blow I've seen is usually the cause of something else happening: either a excessive load due to down lines or a foreign object (an animal, or in one case a thermostat probe touching the wiring) rather than the transformer just deciding in it's own to explode.

Ron,

When the old transformer blew during a thunderstorm it was pretty spectacular. I was at the computer and saw the reflection of the flash on the screen; about a half second later the screen went blank. <lol>

My neighbor wanted to douse the fire with a hose! I'm screaming across the yard for him to stop and fortunately his stream of water wasn't anywhere close the the transformer or he might have been toast. Despite a night of rain the thing was still burning a little 6 or 7 hours later.

As I said, I just wanted to make sure this wasn't a symptom of a bigger problem. Loosing power for three days wasn't a lot of fun.