No,we can be sure, scientifically, that what you think you heard wasn't "some sort of odd harmonic...[or]...a mixing trick...."You should probably start with a good physical and hearing exam. Is ther a history or tinnitus or other hearing problems in your family? Are you obese or do you have HTN? Have you been able to repeat the experience? If repeatable, next time sit backwards and see if moves to your left ear. This would argue in favor of the stereo in the differential diagnosis and against further medical workup. At least on a audiology area. Are you taking any over the counter medications or prescription drugs? Sometimes these can produce humming. Can you elaborate on your description of symptoms such as "tone...unreal and lush but with a slight humming...". Was the tube-in-you- ear sensation accompanied by warmth or the sound of bacon and eggs frying in the distance? These and other questions must be explored before a complete response is advisable or possible. Beyond this advise, for now, you should consult a primary care physician regarding the need for a complete physical and/or neurological and/or psychiatric workup. Best wishes. Email if I can be of further help. I know several fine M.D.s and even one that is an audiophile in the LA area.