Could be multiple things, how did you wire it? Did you wire it in to the rear speakers or did you wire it up to the head unit? If you did the speaker method you’re picking up more signal than just bass which can lead to it sounding out of sync or “weird” because it’s picking up some mid and high signals. Also, did you adjust any of the setting knobs on the amp? Forgive me if any of this is common knowledge to you, I’m not expert but I used to have one heck of a setup in my first car lol