For about six months I have been hearing a light ticking in my engine, it is more pronounced when the engine is decelerating after being revved. About three months ago the ticking became more pronounced when driving in gear accelerating, it turned into a knocking sound. However you could only hear the knock when the car was in gear accelerating, at idle if you revved it with the clutch in you couldn't hear the knock.

I drove the car farther than I had in a while, about 10 miles on the freeway, about a month ago, I left it for four days and when I returned I drove home on the freeway and the RPM needle was quivering, it has always been very steady before, but it was quivering and it was not running correctly.

Ever since then the knocking has gotten VERY loud (like a motorcycle when accelerating in gear), it sounds almost as if there's no muffler/cat on the car, the same way it did after I installed my headers and test ran it with no cat/muffler.

I checked the headers and it doesn't feel as if they're separated from the block.

Any ideas? It sounds like two independent problems.