Crackling through left speakers only?

Recently picked up an old Marantz system - PM 350 amp, EQ 20 equalizer, SD 1030 cassette deck, ST 450 tuner, TT 221 turntable. Don't know the history but they seemed to have been in storage for a while. Problem is when I hooked it up I get clear sound out of the right speakers but cracking out of the lefts. Any ideas?
Unfortunately the cassette deck is dead. Have yet to investigate.
Looking at a marantz CD73 CD player to complete this 80s retro system.
Would appreciate any helpful hints on the crackling and any ideas where to start on the cassette deck.
Not an expert at bringing vintage stuff back to life but: 1st thing I would do is exercise the volume, balance, and tone controls many times back and forth (like 50 or so) with the unit off. I'd get some contact cleaner and clean those same controls. Those things get dirty for sure. I got a 1979 Yamaha R-2000 recently from my Brother and went through the same process and now it's much much better.
inspect/clean volume pot or balance pot.