I have an 87 z28 seems like there's a slight tapping noise coming from the engine it runs a littl3 rough up until you hit 40 then it runs fine ,the bolt that hold the exhaust to the engine came apart while changing the starter but the tapping noise isn't from the exhaust?????

 

It's either a lifter or a connecting rod.

 

In my experience, it was a connecting rod... twice

 

What are some signs if it is a connecting rod???

 

Lifter has a more tinny sound to it and it should be loudest when your head in under the hood. Rod knock sounds more like someone tapping a ball pen hammer on the side of the block, it is a more solid sounding knock. That is why it is called lifter tap and rod knock. The rod knock will be louder with your head under the car than it is with your head under the hood.