Help: SR4 3EQ Fretless Electronics Problem

I own a 2000 SR4 3EQ fretless; last year my preamp died and the battery holder’s wires also got dislodged. I bought a replacement preamp crescent assembly from the factory, and soldered it in, using the same color wires connected to the original. Everything was fine after I soldered all the wires together, but after not playing the bass for several months, I’ve noticed that after plugging it in, the preamp is dead again (volume knob works but tone knobs are non-responsive, and I hear loud noises sounding like squelchy feedback and popping sounds. This goes on for about a minute or two, and then the preamp suddenly works again. What is the cause of this annoying “warm-up” noise? Did I wire things incorrectly? Yes, I am using a fresh 9V battery.