Just purchased yesterday! No power loss or lagging, just this knocking noise. I’m wondering if it’s a piston bearing, ac pulley being loose, or if it’s the timing belt tensioner. The sound goes away when I rev the engine, it doesn’t follow through so that makes me a little less nervous but it didn’t start doing this noise till last night. Didn’t hear this noise of course until the next day. Didn’t hear it on the original test drive. Video of the issue/ sound.