I have a 70's Midas mixer and I was having an issue with white noise coming in through the monitors. Narrowed the issue down to one of the stereo out channels. Not knowing quite what I was doing, I looked for anything that looked disconected, burnt, etc....didn't see anything, so just pulled out the four and so op amps, blew the area where they were connected to the board out with air and reseated the opamps......Problem with noise seems to be solved. Is this likely just a coincidence or could an opamp not seated optimally cause a noise issue? The noise issue was also showing up in the eight busses....the noise rose as the busses levels were brought up, but only when the problem channel was in the board.