Hissing sound under kitchen sink
#1

While in my kitchen one day, I kept hearing this hissing sound like air coming from a tire. When I finally found it, the sound was coming from underneath the kitchen sink. After further investigation, the sound appears to be coming from the hot water line. I can shake the water line and the sound changes with the motion of the water line. There is no water leak and I do not have any gas lines in my kitchen. Please help me find the cause for this noise and a remedy for it. Under my sink, I have partial copper and plastic water lines with shut-off valves, a food disposal with drain connected from the dishwasher and an instant hot water dispenser, along with normal plumbing for a double sink. I know what running water sounds like in plumbing and this does not sound the same. PLEASE HELP!