Also from the traces I can see that the level of hum is extremely low….. is it audible at all? If the traces refer to 0dB as a reference, then the noise cannot be audible.
The noise performance of the input stages are very reliant on the quality of the ground connection on the positive inputs of IC1 and IC2; there is one pin on each of those ICs that is connected to ground. (I can’t tell you if it’s pin 3 or pin 5… I don’t have that info.) If you can establish by examination which pin it is on each IC, then it might be a plan to link those pins so that the ground is the same on each.