amp problems jbl px300.4

Ok so here are is the problem.  When first starting up my stereo today i noticed my left rear speaker wasent working.  At this point i thought it was just a bad connection.  Halfway from my house while driving to school the speaker turned on.  There was a popping commin from the speaker right before it turned on.  It also did the same thing on the way home.  When i returned home i checked all connections as well as the speaker resistance.  All turned out to be a good connection.  I then turned my attention to the amp.  Lookin at it i just started moving switches and messing around with the gains to see if i could locate any problems.  I noticed when i switched the slope switch from 24 db octave to 12 db octave the speaker came on, (this was just the one for the rear speakers) i switched it back to 24 db octave and now the speaker is playing.   Do you think i could possibly have a bad connection in that switch?  But if i did wouldent that cause both rear chanels to go out?  Any thoughts or suggestions would be appericated, thanks  O yeah btw the speakers are 6*9 infinity kappa, the old series (white Cmmd 4 ohm)