Jetson TX1 HC-SR04 Sonar problem

I have several HC-SR04 sonars attached to a NVIDIA Jetson TX1 and they all work well with one exception. If I just have them mounted in their brackets, I get no or false readings most of the time. The minute I touch or hold one in my hand, the sonar runs perfectly. I am assuming this is some type of grounding issue but not sure how to resolve. I have tried several of the ground pins on the TX1 J21 GPIO connector as well as swapping the 5v pins, etc = always the same problem. The minute I touch/hold the sonar, it runs prefect? Any ideas? Thank you ahead of time.

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