Odd engine knocking issue

[firebirdgangsta]

Hello all. I'm new to this forum. I just bought an SVX a couple months ago with 92,xxx miles on it. Also my first Subaru. It was running real rough so I replaced the bad coil packs etc. Then everything seemed to be great. Then I heard a slight "flopping" noise. So I figured I should change the oil since I have no idea when the last oil change was. So I ended up doing a quick Seafoam cleanout and replacing the oil with Mobil1 10w30 and a Fram extra guard filter. And now it's making an odd inconsistent clunking noise. I can't remember if it started before or after the change. It seems to be almost undetectable most of the time. But when I'm parked on an incline it's quite noticeable. I already asked someone if it could be the bearings and they said that it's very unlikely because there's like 7 main bearings or something. The sound seems to be coming from the passenger side head. In another post someone said that it could be carbon deposits on one of the pistons. But that doesn't really make sense with how it's louder while parked on an incline...

Any ideas or advice?

Thanks!