When I say suddenly, I only noticed it yesterday. Amp seems to be overdriving 'too soon' on both channels. Just seems to be a fizzy edge to the sound which Im sure is new. I'm suspecting a pre amp valve, maybe V1 as 1 half is common but just looking for opinions in case rolling valves doesn't identify the problem. Its a later version with the transistor IC for switching. Was last serviced at the factory about a year ago.