Buzzing/Loud overtones on Sansui 2000A receiver?

Hi there,

I bought a used Sansui 2000A receiver a couple years back and LOVE it. Replaced a couple tubes when I got it but it didn't need anything else until now.

Recently there is a buzzing when I play a record through it. It sounds like loud feedback/overtones.

I replaced the tubes, double checked the speaker wire and connections, played different records, and also played the record player through the alternate phono inputs. No dice to get the buzzing to disappear.

I'm playing through a couple of year-old (bought new) Klipsch bookshelf speakers.

Any ideas on what the problem might be?

Thanks in advance,
Mark