Under-car sounds can sometimes manifest themselves far from their sources. Do you have a trailer hitch? Certain makes/models of hitch may bang against the tailpipe. I'd also get them to check for loose heat shields or hangers on the exhaust system. Although you'd expect to hear rattles along with the bang, the Odyssey is so well soundproofed these sounds may not be readily apparent unless you're window is rolled down.
mclarke
mclarke
