Engine knock on initial start up after car sits for a few weeks

145k miles.

I've experienced this issue twice, where I had the car up on jacks for a few weeks without starting the car. Upon starting up for the first time after this, there's really violent knocking/rattling. Both times this happened, I was startled and immediately turned off the car.

The first time it happened, I checked the oil, which seemed low based on the dipstick. After changing the oil, I started the car up again and again had knocking for a few seconds. If I remember correctly, there was no knocking after that.

The second time, there was knocking on the first start up, after a few seconds of which, I turned the car off. There was no knocking when I turned the car back on. This start up was after the car sat for 2-3 weeks while I replaced my engine coolant pump, cleaned my EGR system, cleaned my intake manifold, sprayed my MAP and MAF sensors with MAF sensor cleaner, replaced my PCV valve, replaced my engine and inverter coolant, and replaced my spark plugs.

I haven't noticed any oil consumption, and according to a couple people who looked at pictures of my old spark plugs (link -- click), there didn't seem to be signs of anything unusual. No "oil deposits" or anything.

Any ideas? I don't wanna go digging for a problem if there's nothing there, but it's just been on my mind and I'm curious about what's going on.

 

145k miles. Sorry, forgot to include that. Added now

 

In short, no.

The first time, I thought it had to do with an EGR valve replacement the dealership had supposedly done for me when I complained about rough idling while at the dealership for warranty work. So I dropped it off at the dealership the next day, but they apparently didn't find anything at all. No noise or anything.

The second time, I wasn't able to check for codes immediately, but when I did, there weren't any codes.

 

I forgot to note in the first post that while the dipstick showed low oil after the first incident, I still ended up draining over 4 quarts of oil (can't remember if it was closer to 4.5 quarts or not) when I changed the oil immediately after.

Meant to say "no codes."

Seems stable, but I haven't been regularly checking it

I was under the impression that I've experienced the cold start issue and knew what it was, but the "knocking" I'm referring to in this case/these 2 cases was a lot more violent.

I hope it's not a leaking head gasket, but it very well could be... What are signs to look for? Would there be any signs on my old spark plugs?

 

Just found this video. If I'm remembering my noise correctly,it was the same as can be heard at 1:11 in this video: