Sorry to hear this. One knock on all redline products is that they clean so well that it "can" cause something like this to be worse. Same thing with their fuel tank cleaner, every once in a while you will get a guy who unclogged something and gets it stuck in the filter and actually caused a problem because of how efficient the stuff is. Esters are crazy good at cleaning, so it is quite possible it cleaned some slime off that was coating the lifters. Total guess there, but it is possible. I would try another oil as I doubt it's exhaust if soon as you changed the oil it got noticeably louder. If a different oil doesn't make it better, start considering going up in weight and turning of mds. but first take it to the dealer and find out if you have a bad lifter.