First find the exact preload. With any particular cyls' lobes on base circle lay one of those 6" thin steel metal rulers, the ones with the clip to go in your shirt pocket across the valve cover rails & wipe the edge of it with a magic marker then before it dries quickly slide it over till it touches a pushrod & makes a thin magic marker ink mark on it. Then loosen the shaft holddown bolts till the pushrod is up all the way but not loose enough to where it is falling sideways (in the same plane in other words) & make another new mark then take the shaft/holddowns/pushrod all the way out & with that steel scale measure the distance between the two marks for your preload. Those shims will change the wipe pattern in addition to the pushrod length needed. You need .020" - .030" preload and an acceptable wipe pattern (as close to the center as possible/not going off the edge). mancini & others have those metal shims, just me I think they're hokey & I prefer soft copper or alum washers. For the cause of the noise you might have inadequate preload or one or more of the lifters might be defective