I got to school, all was well.

After school I hit a speed bump and heard crunch, apparently my downpipe now hits the speed bumps at my school.

I thought nothing, but a few minutes later I turned off my radio and at about 1k-1.5k RPM and only there, it rattles, sounds like something is loose or a constant ticking.

I have no clue what it is. Can anyone give me some ideas?

Could anything be contributed I do not have my rear O2 sensor yet? It is coming in the mail. Causing issues with A/F or anything?

Thanks.