Some synthetic textiles just soak up/retain some odors (e.g. perspiration and synthetic blend clothing). See if it dissipates after more washings and yeah...try the vinegar.
You're washing with a "Microfiber Detergent", right?
Other than that I'd try to live with it (easy for me to say I suppose, but this could be worse IMO...what if it were some really *nasty* solvent-smell?).