Mark Levinson 585 Noise

Hi,
I'm owner of amplifier Mark Levinson 585.
From the very beginning, it used to happen that when switching on from standby, noise appeared on the left channel. After turning it off/on again the noise would disappear. After a while turning off/on doesn't help and the noise is constantly present.
I'll be grateful for any help, and if any aditional info need please ask.
In attachment is recorded noise on left channel