Normally to me a high pitched whine would be an air leak. Or maybe that's more of a hissing squeal??
It's a tough question and just about all of the Big Box store vacuums from Hoover, Shark, Eureka and Dirt Devil all sound about the same!! They all have loud, higher pitched sounds or at least that's how I perceive it!
I used to run Tri-Star machines that were trade ins in my Filter Queen Office. They were quiet. I think there was a little high pitchness to them but nothing extreme. Honestly I wasn't very impressed with the suction power of them though. There were 2 Tri-Star MG1 or 2's they were. Brush roll wasn't bad but I didn't like the suction of either and bags were in good shape.
****We weren't allowed to clean the office with a FilterQueen cause the boss believed they were the best and he wanted dirt to still be pulled up by Filter Queen in office trainings!! The Boss used to use an Oreck XL21 when he cleaned but whenever I cleaned I chose one of the trade ins cause I didn't like the Oreck!! Not only its performance but the Orecks send me into bad allergy spasms.