Change out the tappet cover gasket, unless they are in the side of your head. If that is the case then it is most likely that your plugs are fouling with oil due to either worn rings or leaky valve stem seals.
When you turn it on, do you hear a whirring up of the fuel pump? Just checking for volts doesn’t always mean it is working. If you don’t hear the tell tale whirring it’s probably shot. Check it for codes first see what comes up and go from there. If codes, fix them first. Reset and test until no more codes. Otherwise it could be a corroded ground. Check all your ground points. Check all your fuses.
I have the same vehicle. What I would do first is hook it up to an OBD2 scanner and check for codes. Also call a dealership and have your VIN handy, ask what recalls need to be performed on that model. Ask if any have been done on that VIN. Mine had 4 outstanding, one involved the rear handbrake not securing correctly. Recalls need to be fixed by the dealer for free. After scanning for codes, check to see if any relate to your transaxle or transmission. If no codes, good. But check anyway. There will always be some play in the prop shaft. Get up close to the u joint and rock it there, see if the caps are loose or there is excessive wear there. if there is replace it, you have nothing to lose by doing that but everything to gain. See if that changes the sound. Check for fouling at the brake rotors, and check drive shafts for fouling also. It is possible that incorrect wheel alignment that caused your inner edge wear, has also caused your uni joint to wear out.
It could be the actual belt that drives the pump. Or a seized idler pulley. Pumps themselves do not usually makes that noise, unless the bearing in the pump is shot. Lift the bonnet/hood while engine running and in park/neutral with handbrake/park brake on. Then watch the pump pulley as it spins, have an assistant turn the wheels slightly side to side. With engine off, twist the pulley belt sideways to check flex and slack. If you can turn the belt 180 it is time for a new one. Also check the pulleys and idler pulleys with engine off by just grasping them and trying to wiggle them by rocking them back and forth in a top to bottom position. Your're checking if they will move forward and backward in either a 12/6 or 9/3 position. They should be tight in that regard.