Darn knock sensor
Some people also do poly motor mounts to stop the y-pipe from banging.
As far as I know the y-pipes banging have never caused the SES knock sensor code. You might just have a bad knock sensor. They usually go out after about 100,000 miles.
It was the Mufflex Bump stop, but the poly motormounts and Trans mount seem to be better. If you dont want them on to you can turn off the Knock sensors, but your SESlight wont go on if you have any type of knock

