Fostex 250 problem with loud bass hum that's Maxs out the meters

[Brutalpheasant]

I have a fostex 250 four track that works fine for awhile, then one of the meters will blast out a loud bass hum, the meters will be all the way in the red. I can tap on the meter sometimes and it will stop. Then another will distort out with the hum. Is this a meter problem or something loose? This is so frustrating!!