The odor that plumbing material may give is generally termed as "waxy plastic citrus," "fruity plastic" and "burning plastic."  Amongst  the various kinds of plactic pipes available, its known that, cPVC has a low odor potential and it doesn't seem to release many organic chemicals. HPDE actually had the highest odor production, although it doesn't release very many organic materials. The PEX-b pipe had a moderate amount of odors and also a moderate amount of organic chemicals that were released into the air. PEX-a had fewer odors and organics release than the PEX-b pipe.  

It would be wise to ask neighbour as to what kind of pipes they use and whether it is giving them any problem or not.