HELP : 1999 civic si rumbling when in gear.
 

Hi, so my 1999 civic si has just gotten back to me from the shop. They replaces my wheel hub and my wheel bearing on the left side and also fixing the exhaust since it had a hole in it. So my concern is that my civic makes some kind of rumbling noise when I press the gas.. it makes my car sound like a boxer engine.. I don't know if the shop replaced the whole cat back or I don't know. When i press the gas while I'm driving, it makes a rumbling noise like something wants to come out or is stuck in the exhaust pipes.. Please help!!! Thank you so much!

Oh and also, when it makes the rumbling noises, the Engine light on my dash flashes on and off.

check for codes it could be engine missfires