Recently I had my pre-cats removed from my 07 TL-S and replaced them with a magnaflow resonator and an aluminium straight pipe. Ever since the replacement, there has been lots of cracking sounds from under my car whenever it is turned off. I even hear it sometimes when I am at a red light and my windows are rolled down. It could be the metal shrinking from cooling, but it's getting louder by the day.

Is this normal? I suspect the guy who installed it did a crappy job.

 

Maybe loose and you can hear it when it expands and contracts.

 

Pre-cats removed and replaced with magnaflow res????
maybe our terminology is a little mixed up here.

there are two primary cats that exit from the heads.
Here's how the exhaust flows:
Pre-cats-->jpipe-->3rd cat-->midmuffler-->muffler-->tips

what I think you did was take the 3rd cat and mid muffler out.

 

Yes, you are correct justnspace.