Hi newly registered to the forum (but have visited it a lot via Google searches). I have a Scag 48" hydro SWZ48A-17KA, with the Kawasaki 17hp twin made in 2003-2004 (according to Scag) that is making some strange noises. I'm hearing what I'm pretty certain is an engine knock at idle, and was ready to start hunting for a replacement. I pulled on the chain that releases the drive belt for the pumps and low and behold the noise is gone 100%, idle through hard rev, blades on and blades off. I took everything apart from underneath related to the hydro drive. The idler pulley wasn't loose or wobbling - but making faint ticking noises and had the "feel" of being unbalanced (could just be me though) when spun, but the pivot arm bearing(s) were pretty stuck. After un-sticking them with wd-40, I put everything back together. The second I released the chain the noise started again. The pivot arm moves about 1/4 of an inch back and forth while at idle (normal?). I've read threads (not for my exact model but I'm trying everything) that said to check the small drive pulley that may have worn out the keyway or that my pistons may be carboned up. I would "think" that engagement of the blades would certainly be more of a load than the pumps (but maybe not because they don't engage at idle?) It purrs like a kitten with and without the blades on but the second I let that chain loose for the pumps it starts again. Has anyone ever heard of the idle pulley causing these horrendous noises? What kind of compression numbers would tell me if this (carbon buildup) was the case?