Hi, I understand what you are going through.. it's very frustrating, I thought mine was stress related as I was overworking at the time,my Doctor told me that my original scan was clear,my noise/pulse went away and became less frequent, anyway after having a scan for a more serious matter (unconnected by the way) the Doctors discovered that I have a high riding jugular vein/bulb? which is probably the cause of my occasional problems.
Mine went away and returned less frequently,BP is now normal,pulse is low and I still get it.. no set reason that I can find apart from their explanation.
Try and not focus on this,avoid meds, exercise to relax if you can and do use a fan on low setting to cancel out the noise, it worked for me and I really don't even think about it now, in time you will get used to it, good luck, Pudd