help! Kustom GRovvebass1200

[inebriatix]

i am completely new to talk bass so i hope i am posting in the correct place. i have a Kustom groovebass1200. its a older model with the blue jewel. think around the second year of production. i am running it through a behringer 115 cab with a new eminance delta lfa 8ohm watt speaker. bypassed the tweeter and just ran straight to a new speakon jack i mounted inthe back of the box. so i am not running any crossover since i dont have a tweeter goin in it. after getting all this rigged up and playing it for about 20 minutes at a decent volume, i noticed a sound issue. not buzz or hum really. it was fairly silent when i was not playing my bass. more of a wahhing mean synth sounding distortion. i tried a different bass and bass cable. it did not change much when i adjusted the master volume and gain. i dont have an extra speakon cable to try runnin through the back. and i dont think i blew a speaker but i am not sure. it doesnt sound like that kind of distortion. kustom was not as helpful since they make a new head now. really hope someone can help