hi! same problem with my baby monitor also bought in the US. was able to use it only a couple of times then the loud static/interference began.
my friend checked it for me and said there is problem with the "grounding". was able to fix it and it worked a couple of times then the problem re-appeared.
still have the same problem until now and i stopped using the monitor such a waste of money
may i know what brand are you using? mine is graco