I would be looking for a break or loose connection first, bad drop, start with the basics man, you know that. Does the noise show up at exactly the same time frame or is it intermittant? I had something like that more than once and there are any numbr of problems and solutions..I had one run me one day and it turned out to be a loose housing to housing right off the first amp out of the node. I never picked up a leak there until one day when the wind was blowing strong one day. Look for leaks.
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