This is an unusual problem that has been bothering me on and off since I put the Gulfstream unit into operation some time back. I have thought that the unit was noiser than it should be all the while but at times it seemed to be louder than outer times. Last year I removed the fan motor and inspected it quite well but was unable to find any real culprit that glared at me as the problem. I greased the bearings a bit and put the fan back together and the noise was better but STILL NOT PERFECT. Even though it was better I was not pleased with it but lived with it till just last week. The heater rather suddenly started making quite a bit more noise than it had ever made in the past. It was bad enough that I turned it off for fear of something being damaged. Well I started inspecting and disassembling the fan motor to check any and all possibilities but here again found no glaring solutions to my problem. The sound was like something banging metal like noise. Not like a bearing going bad and the bearings looked good. I thought it was the compressor making the noise after I was unable to find that the fan blade was hitting anything but I could not make myself believe that the compressor was making that noise. Just did not sound right. Read somewhere in researching this issue that the hub could become loose on a fan blade and that it should be checked. Well I did check it and did not seem like there was a significant amount of play there that would cause such a loud noise as was being made. But after exhausting all other possibilities I revisited this issue and was able ot tighten up the fit of the hub to the fan blades with a hammer and wonderbar by pounding the hub where it was pressed on and was holding the blades. As it turns out the noise was eliminated when I turned the unit on again. In fact it was quieter than it had ever been since I had it. Needless to say I am very happy about this problem being solved but the SILENCE IS GOLDEN!!! A simple fix and didn't cost anything at all but some time. It is amazing that such a small amount of play in that hub could create such a loud noise and vibration. Hope this helps someone else who is trying to chase down a noise in their unit. Mine is whisper quiet now!