We have an old (older than me) Sony Trinitron XBR TV and it has detached speakers, with two leads to each. Occasionally, out of nowhere it'll just buzz and crackle. Does not matter what the volume is or what the source is, it'll make the noise at the same frequency and volume.

Is it just that the TV is too old? It has an incredible picture for a TV it's age though... it has put to shame every other tube TV we've owned to shame.

 

Does this happen with multiple sources?

 

Hum can be bad connection. Make sure everything is tight. If it still hums then probably a bad solder joint inside.