Possibly RCA's Going Out On That Channel Or Loose Connection At The RCA's. This Could Be At The Headunit Or The Amp. Give The RCA's A Little Jiggle At Both Ends And See What Happens. You Could Also Have A Short To Ground In The Speaker Wires. Happy Hunting!!

CSVT E0 3L 14.5 @ 94mph, Stock Intake, Stock Exhaust minus Resonator, CEL, And Broken Pass. Side CV...Untuned.