hey guys, any idea how much work it is to change an oil pump on a 4.6. and at 110k miles, do I need to change my oil pump? I heard a grinding sound two different times I started the car. A warning message "check oil pressure" came. I switched off the engine and started it right back and everything was ok. So hence the reason i was thinking its the oil pump, OR i'm not sure if it's the timing chain. Any previous experience or ideas would be greatly appreciated, Thanks...