I already know that these Titan electric tankless units are basically crap, however I did not install this one. I recieved a call from a customer of mine complaing that after I had drained the water lines and sweated in a 3/4" by 1/2" tee 3 ft below their tankless....they are now hearing a weird noise. I went to the house and determined that when cold water is used anywhere in the house, the pressure drop at the tankless causes a weird noise. I'm guessing that it's creating a vacuum?????? They say that it wasn't there before I did my work, which made me think MAYBE I had cause some damage to the flow valve inside the tankless with the hot air inside the pipe when I was sweating(IF these even contain a flow valve) . There is plenty of hot water just as before my work. Any thoughts?