[hypoxia]

Thanks for your ideas although I came up with a different solution.  I found two adjustable air valves with a 90° 1/4" quick connect output in my supplies, replaced the noisy valves with them.  Then I dug into my water softener/RO supplies and found a 1/4" Y push connect fitting.  I fed both exhaust valves into the Y and used the single output of the Y to feed my muffler.  I took an oil sample bottle (thanks Blackstone Labs), drilled a bunch of holes in the bottom & stuffed it full of foam.  Then I drilled a hole in the cap and put a 1/4" push fitting in it and Voila! I cannot hear the door open or close.