I have a 97 F-150 with duel exhaust side exit/ the Y pipe has been eliminated, still have all converters, when the truck is idling the exhaust sounds like air puddling- don't know how to describe it - muddy, airy, not good . I have to 40 series Flows -sounds better when at higher RPMS - any ideas - these are new, I find no air leaks- truck runs great, no cel. Any ideas on how to correct this?

 

Its probably just the way they sound. They do give a hollow and faint air sound at idle. Verify you have no leaks though, let it idle, crawl under and carefully feel for any loose air escaping from all the new welds that were added.