Several problems at once.

 

I have had that off and on for years

My car has over 117,000 miles so the flex pipe is likely overdue for replacement

 

Strangely enough it did sound like it was coming from under the hood

 

When the engine can't control fuel delivery it can create a misfire to be detected although may not be felt.

 

I am bringing my car in to my buddies shop I showed them the codes and the owner didn't think it was the flexpipe so we have a friendly bet But near impossible to drive Accelerates very slow and loud and will not go above 50 mph

 

That severe a problem is not flex pipe alone. There's something else going on besides that if it's even bad. We are guess winging it.

 

What I am hoping is that the leak is creating a lean situation which is causing the car to be in limp mode. If there is a leak right before the O2 sensor, then the reading will be way off

The car was running fine until 2 days ago when this suddenly began

 

Greg, have you ever drove an HHR with a flex pipe leak, it is noisy and loud and causes engine and fuel management problems as the leak is ahead of the O2 sensors, thereby causing an injector to fire lean or rich.
Ive had flex pipe failure and just replaced the complete down pipe including the catalytic converter. Usually the CEL will set P0420 and P0172.
Once this is fixed then we suggest retesting the codes and deal with them one at a time.

 

P0326 is caused by the misfire.
P0171 could be, too.

 

Here is the insanity Our flex pipe is only 2 inches long On most cars there are flanges on each side But on our cars, you need to replace the ENTIRE down pipe and the catalytic converter. One shop quoted me $800 to do it
The other option is to cut the pipe and weld on the new flex pipe But that will also be expwnsive

I am going to try wrapping it with fiberglass exhaust strips and see if that works