2003 Mitsubishi Lancer 150,000 miles, manual 5speed, no check engine lights. This car has been sitting for about a month or two and when I tried to start it, it wouldn’t start so I eventually tracked it down to a fuel pump relay and it started. But when I started it it sounded like it had rod knock coming from the back of the engine near the either #2 or 3 piston, I couldn’t tell if it was coming from the oil pan or near the piston more but it was definitely from the bottom end. Anyway I let it run for about a minute trying to listen to where the sound was coming from and giving it some slight revs to see if it was rpm dependent (it was) and to see if it would go away (it didn’t) so I shut it off thinking the engine was cooked then about 5 mins later I started it up again and it made the same noise but quieter, let it run for about two minutes and shut it off again then the third time I started it it was almost gone and after letting it run another minute or two it was completely gone and I haven’t heard it since. I’ve gave it some beans when I drove it and it feels normal on power. I changed the oil about 2,000 miles ago and and made sure it had oil before I started it. I’m just worried that there could be serious damage any advice would be great.
I don't think it's much to worry about. More than likely all of the oil in the engine settled out and was in the pan. When it hasn't been run in a while, everything has minimal oil, so strange noises are going to occur. Then once oil starts getting up in the nooks and crannies, the noise abates. I wouldn't like it either, but it is pretty much a fact of how it works, especially with an engine which has a few miles on it.
Overall, as long as you're not experiencing any issues with how its running now, I wouldn't worry about it too much. Yes, you can imaging there's a little bit of extra wear associated with this and you'd be right for thinking so. However, there's little you can do about it now. Plus, the amount of wear associated with this even should be fairly minimal. In the future, just don't let it sit for so long between startups and you'll most likely be just fine.