I hear a quiet Bass in every song

Hi,

recently i've heard some strange noises coming from my Controller... Sounds like it's playing the Baseline few times. Don't know how to describe it.. it goes bum bum bum bum.. but very quietly... could it be software related? i use Serato... but on my djay pro for mac it doesn't make any noises?? i connected ddj sr through booth out on my aux..

hopefully somebody can help..
Thanks in advance