97 impreza 2.2l coupe on start up there is a engine knock until the car fully warms up and then its gone

THis could be several things. Start by making sure that there is nothing under the hood that is hitting the belts or pulleys. Check the oil level. If the oil level is low, add enough to top it off according to the dipstick. If the oil is okay, look to see if it is dark, thin and runny. If so, change it and the filter. If that is all okay, it could be a valve or lifter. Watch for oily spots to show up on the rear bumper which would indicate that you are blowing oil out the bottom of the engine - not a good thing. Also watch for smoke coming out the tailpipe after the car is hot - don't confuse steam in the early morning's cool air with smoke.