Mark levinson no 26 Rustling channel

Hello! The preamp Mark Levinson no 26 rustles one channel on a black background. what could be the problem? He recently underwent preventive maintenance with replacing old capacitors with new ones, but there is still rustling at all outputs and even in mono mode only one channel rustles. What advise to check? This rustling is not particularly annoying, but I really love this preamp and I want it to work like a Swiss watch 🙂.