A few days ago, I took the stock air filter out to see if it needed to be replaced. When I put the rubber tubing back on the throttle body and air box, it didn't seem to fit right.
After that, the engine made an awful noise on cold start, sounded like maybe the water pump bearings were going bad. Wasn't quite as bad after the engine warmed up for a minute or so.
Come to find out I put the rubber tubing on backwards and it wouldn't stay on the air box.
There was a gap between the air box and the rubber tubing where the air was being sucked in.
I found a picture of the air intake on the site and that'* how I realized I had the tubing on backward.