I recently picked up a 4-way air manifold from eBay (http://cgi.ebay.com/4-way-Co2-Gas-distribution-manifold-w-Check-Valves-/300387099465?pt=LH_DefaultDomain_0&hash=item45f0776349) and after hooking it up, I've noticed a very loud whistling sound when air flows through it. Any ideas what would...