If you do a AK search, just over the last month, there have been a number of MC2105 and MC2100 (no meters) posts with owners looking for answers to their 40 year old amps issues.
These amps are 20 years or so beyond the expected service life of a typical capacitor so a recappping is past due.
Most likely a noisy transistor is beginning to show it is going to be a upcoming problem, but without a thorough bench test I am just guessing.