Weird hissing.
If its pipe definately use the teflon past or the thread sealer. be sure to let it dry for a bit before putting pressure on it. Also...once its set or dry...do not spin that piece ever again or you will induce a leak by breaking the bod of the sealer.
If its flared AN fitting its supposed to seal on its own. I would relive the pressure...take it apart and clean up the mating surfaces a bit and put it back together tightly.

