Anonymous
I have investigated such sounds right at the Switch and have found some cases that it is the Feed line rubbing on supports. The fix was to adjust the pipe hangers and supports which did mitigate it. Check your line hangers and supports and look for rubbing marks. You would be surprised to see how much you lines move either from thermal expansion of the line for from Coke Drum Moving. Not sure if you found your problem or not but please share your results if you have. Thanks! Coker Guy