That sounds like an overheating problem.
Make sure that the PSU gets all the ventilation it requires and that the regulators are properly tightened on the heatsink
Sources: Modified SL1200 MK2, Salas folded RIAA, Phonoclone, VSPS, Shelter 501 MK2, Modified Pioneer P6D6 as transport, Shigaclone transport, Peter Daniel NOS DAC.
Amplification: Custom 211 Monoblocks, Electrocompaniet AW120, Audio Research VS110, Gainclone
Loudspeakers: Tannoy Turnberry, PBN Montana EP Signature
Cables/stands: Tempflex ribbon and Twinax cables
Other: Promitheus Signature Passive Attenuator, Custom JFET - transformer preamp.