My vehicle is making an awful knocking noise?

I'm a delivery driver first of all. I drive a 1999 ford escort. We'll today on a delivery I was leaving a customers house and when I put my car in reverse I noticed a terrible knocking noise coming from my front end. When I got out of the driveway and put it into drive it died on me, this happened 4-5 times before I finally got it to start and drive.
We'll when I started driving the knocking became louder, but when I let off the gas it stops. It wouldn't go much over 35mph unless going downhill. So I pulled off at a gas station a few miles up the road and when I pulled beside a pump it died again.
When in park/neutral it sounds fine, but when I put it in gear if I don't give it gas it will die and when I do give it gas it makes that awful noise. I thought it could be my lifters but I checked them out and they are fine. The sound is coming more from the bottom end of my engine.

Also I don't know if this matters or has any relevance, but when I put it in gear my engine lifts up about 6-7 inches. And taking it out of gear the engine goes back down. I need some help or advice, I'm not much of a mechanic and I need my vehicle running again As soon as possible. Any advice or help would be much appreciated

This is commonly referred to as "the sludge issue". I have always taken issue with the use of this term to describe the condition.

I think this is translation error from German to English. The issue is oil deposits, in the way of black flaky particulates, building up on the inside walls of the crankcase and crankcase ventilation system.

If you remove the oil filler cap and look at the underside you will likely see the buildup of these deposits. Over time these particulates flake off and work there way down into the oil pan eventually plugging the oil pick-up screen.

This restriction in turn restricts the passage of oil to the point where oil pump can no longer supply the specified quantity of pressurized oil to the system. The oil pressure warning system, picks up on this lack of pressure, illuminates the light and sounds the warning.

After confirming that there's an oil pressure issue the extent of damage to the engine, if any, is determined by inspecting the camshaft journals (bearing surface) for any signs of lubrication failure.

This is the first component to get damaged if oil starvation was excessive. If the journals are OK repairs would consist of cleaning the crankcase, replacing the oil pickup tube with strainer or pump/strainer assembly, replace oil feed line of the turbocharger, replacing All crankcase ventilation system hoses, pipes and pressure regulating valve as described in the service bulletin.

Then a special engine flushing system would be hooked up to the lubrication system and flushing procedures would ensue. After which the vehicle would be restored to running condition.