phantom engine growl at 110km/hr and -20 C

Growling noise (compressor-stall-related noise) is induced by the partial reversal of the charge air in the compressor wheel. Partial flow separation at the suction side near the blade outlet causes the growling noise. Its frequency ranges in a wide band between 1,200 and 3,500 Hz containing partly metallic noise, and occurs at engine speeds between 1,400 and 2,500 rpm in second and third gears. Growling noise propagates in the direction of the compressor outlet, and the charge-air intercoolers. Found this. Maybe helpful.

That is the first answer anyone has been able to offer me that makes sense! I'm extremely grateful, but is there any solution to curing it and is there any possibility of engine or compressor damage the longer I drive it while it intermittently comes and goes? Thank you for your help Mark and any advice you might suggest!

Being 65 years old my turbo knowledge dates back to the mid 60's when we had a local drag strip in our area where young men could build their own rods to drag. However, speaking to a retired Ford mechanic who is my age he offered the following. 1.) Ford recommends the use of 91 octane gasoline, although it suppose to operate on E85. 2.) He questioned whether the problem existed with the outside temperature was above freezing. Usually the hotter the outside air temp, the more problems one has with turbos. 3.) Not being quite sure, he believes your vehicle may have twin turbos. Adding they are extremely expensive to replace and should be replaced in pairs.. Not ouch but OUCH-OUCH. 4.) Since the growl is intermittent and when the vehicle is moving it will be difficult to diagnosis, as the device is mechanical and not electronic. NOTE: We're from the deep South where we consider any temperature around 50 degrees F an polar blast. He does remember something about engine growl in turbos operating in warmer temperatures associated with transmission gear and RPM. You may want to research in that direction.

In Alberta Canada our outside winter temperature is minus 16 degrees Farenheit and the growling noise usually occurs during winter at any given temperature. I had it happen at +20*F but not often. I am concerned because this is occurring much more often and for longer durations where, when new it happened only rarely 2 or three times in a 75 mile trip. The 3.7 litre Ecoboost V6 is the first twin turbo engine Ford put into production in 2011 and I'm frightened to hear the possibility of replacing them in pairs, if that is indeed the source of the howling noise. Thank you OJ and Mark for your advice as I hadn't been told 91 octane fuel may be better for that engine. Our regular gas here is around 85 octane, so maybe it's time to trade it off before any serious repairs happen. Again thank you guys!