How can you tell if the diaphragm is bad? This was on the car when I got it and it only has the large spring in. Was overadjusted so I backed it off and used the recommeded adjustment (2 - 3 turns after contact). No more surge (flutter), however, no I get a weird "Ding" noise shortly after the valve has operated.

Also does this when crusing at 25-30mph and the vac is about 14-16in/hg.

Any ideas?