Put the smut to one side, my helmet has developed a whistle. A slightly more than motorway speeds on the right hand side it whisles. An AGV Ago, nothing fancy which has been fine for years, 18 plate DVT Multi, no change there. I have the hearing of a fifty year old so no problem there. Doesnt make sense. Any clues or answers please.
Whistling is usually due to the visor not fitting snugly to the helmet shell. Check where it seals against the visor openings for any gaps.
Some could see it as a bonus having a helmet that whistled when you went in the right side! On a more serious note a couple of things to check - if the rubber round the visor edge come unseated or if there is something stuck in one of the air vents.
Have you lubed your rubber recently? Used to get a little bottle of it with Arai lids to keep the seal supple.
Sent an AGV back for it. I found the source was the visor and tried to adjust it, but thought why am i fixing a brand new helmet so sent it back. Sorry to say will not look at another AGV now