Engine Tapping

Not sure on the speedo.

The night light? PArking light? If you mean parking light, you probably need a bulb. There is a double filiment bulb that will light when brake is on and slightly dimmer with the parking light.

Would you call the knocking a rattle, like marbles in a tin can noise?

Is is possible that the exhaust moves into a postion that is is bumping the floor? OR a heat shield that is moving at the higher speeds? Stick you nose under and do a little feeling around for anything that may be loose.

You'll need to check for power and good ground back to that socket if the bulb is good and installed correct. Sometimes there is a ground tab that needs a little manipilation.

Not necessarily. When your in fifth gear, you are running at higher speeds and have an increased air flow throughout the car. IF you stick your arm out the window with a loose jacket on you'll see how the sleeve flaps like crazy. Now hold you hand out flat and slightly pitch it like a flap on an airplane. You whole arm goes up and down as you change your flap. Err hand. Transfer that theory to the car. A loose heatsheid that is thin will do the same. It may be pushing up on something such as a hose. It can be moving itself or somthing else and hitting the floor board or anthing that transfers the energy to your feet.