Yes, the early potentiometers can be an issue with these. They work via voltage instead of signal, the voltage drives the resistor ladders, so when the pot becomes noisy, it translates into a fluctuation in the output level.
There is now an updated pot & PCB that have proven to be more reliable, these are updated on all 112s & Nait5s as required during a Naim repair/service.
Regards
Neil.