I have a 1996 with a regular system (not JBL, no sub, with autoset button before upgrade). I have used a Pioneer FH-P404 head unit for about a year. However, recently I noticed the rear left speaker only puts out most lows, no highs, and the right almost no sound at all but a buzzing when I put the balance to the rear. I thought it was the speakers, so I bought two Infinity Kappas to replace the back and eventually I'd replace the front. However, I get the same result with the Kappas. I know it isn't the speakers, as they're brand new.
My question is, is there an amp in the rear for the stock system that may be causing this? If so, will buying a harness to bypass it solve this problem? The Pioneer unit has a built in 40x4 output, by the way...
If my car does not have an amp, what may be causing this? It is very frustrating...