The answers you have gotten so far seem not to help you. This is because the information you gave with your question does not help finding the right way.

If you could show that how you did "think through" the problem (I don't know if this is the right expression), e.g. by answering these questions, … or by telling us how your problem arises in the first place (what makes the signal appear?) - this would greatly help finding a useful solution for you.