other one could be your hot water heater and they should never really be that close to each other and if it happens to be gas it could be worse and if it is from a dryer even worse .Did you have a house inspection ,inspector should have noted those 2 vents and checked what they are .My son is a home inspector for a company up in NJ besides all the other things he does .Welder ,tow truck driver , diesel mechanic licensed electrician ,tattoo parlor owner and he had a remodeling company in VA for awhile until his divorce