cassie: Noise can be from several things. To isolate it can be a bit of a challenge. If you think it is a lifter, you can try the following.
Set idle as low as you can. Remove valve cover and with a bit of practice you can adjust each valve with the engine running. A 5/8 short box end wrench will loosen the lock nut and a stubby screw driver will make the adjustments. You need to develop a "limp" wrist to do this but it is not too hard to do. Start at the rear, #6, and loosen the nut and tighten the adjuster 1/2 turn. If the motor slows down or stumbles back it off until it is smooth. Repeat for each valve in sequence until you find the noisy one or they are all done. If this does not stop the noise you most likely have a bad rocker arm, push-rod, or lifter. Possible bad arm on the fuel pump. This works for solid lifters as well. But it is hot and messy so only advise it for troubles like yours. Keep the idle as slow as the engine will run. After the nut is loose let the wrench "float" so it will not clatter and won't push down on the rocker arm. Do this when the engine is warmed all the way up. Also a good time to look at the oil flow at each rocker arm. I think you will find the noisy lifter and I think it will adjust to quiet. On the one that is noisy you might need to turn the adjuster a bit farther But stop if the engine slows or stumbles. That would mean that the valve is not seating. The trick is to let the valve set on the seat and take out the mechanical clearance from the lifter, push-rod, rocker arm, valve stem, and cam. You will be able to do this and hear if and when it makes a difference. When you are done set the idle back to 450-500 RPM put the valve cover back on and see if it stays quiet. You might have a bolt from the coil mount rubbing on a push-rod. To tell if it that, you will have to back off the bolts 1 at a time while it is running. If that makes the noise go away use a shorter bolt or add a washer or 2 to the bolt that is rubbing. I would start with the bolts to the coil. Should have put that first.
