When going up a ramp or overpass (not going fast) I hear a knocking sound coming for the engine(85K miles). When I accelerate the knocking stops? What could cause this?

Are you sure it is knocking? Sometimes I can hear my fuel pump working and it sounds similar.

Conduct an experiment. Try using high octane fuel to see if it goes away. If it does, it is pinging. It could be a clogged EGR valve, and it could be a faulty knock sensor.

Is your “check engine” light on? How old is the car?

What year is this Grand Marquis? Not all years have knock sensors. I had to run 89+ in most of my Grand Marquis to keep them from pinging.

It’s a 99 w/ 85k miles. Last year I changed the intake manifold (due to cracks at the Thermo. housing and have replaced all ignition coils for the spark plugs. I put in a can of Seafoam last week into the fuel tank. the egr valve seemed ok last year, but will recheck. Thanks

I have a '98 Vic that does the same thing, but not all the time. The rattling is not that serious so I just live with it…Like you said, you can control it with your right foot…