This xD is used daily and it has right at 172k miles. I've been having to replace the spark plugs & coils every 6 to 8 months since 2021, due to a misfire. Always cylinder #1. So about 6 months ago, Toyota installed a timing chain tensioner. Now there's this "ticking" sound coming from behind the valve cover, or so it seems and it has become louder and louder. I thought it might be an exhaust leak, but doesn't appear to be.

To me this sounds like a timing chain problem, or perhaps a valve problem. It idles "ok" but runs rough. With this many miles it could be a number of things. I'm just looking for some direction. It's a 2ZR-FE 1.8L