Rather limited amount of information available about the bike.
We know: Street Glide, Growling noise when two-up, tire tread & pressure OK.
How big is the passenger? any chance that the rear tire is rubbing something under the fender?
Bearing ? , brake disk or pad rubbing ?, tire cupping ?, Tire rubbing under fender?

 

FWIW the rubber mounts you are discussing have nothing too do the belt tension as the swingarm is mounted to the transmission through spherical ball type bearing from 02 up.. 01 and earlier had a different bearing.. Those bearings would have to be bad for the belt to loose alignment.. When the bushings you mention wear out, the whole rear of the drive train can wobble.

As far as noise in corners, tires would be my suspicion.. Michelin Commanders (the first version) were real noisy in the corners even when in good condition. When wheel bearings go bad you can hear em when going straight too.

For sure, it's worth having someone look at it if unsure of the source..

 

My 13 does the same thing. I was told it was the tires. I guess I'll know for sure when I replace them.

 

Yes I see your point the tranny is fixed to the swingarm so my theory on the belt rub is wrong, but what about the rest of my post around alignment? Depending on the year, he should have a heim joint at the top of the engine to the frame and another at the front of the engine to the frame. Again when the rubbers fail the vehicle alignment is affected and when alignment is out, you get vibration, maybe growl.....

 

My 09 Street Glide did the same thing. Replaced front tire when it was worn, it stopped. 10k miles on the new one, and it started again. Replaced it when worn again with a Michelin Commander II and haven't heard or felt a vibration since.

 

I have a slightly used set of Michelin Commander II's I would gladly sell..... Front and rear, couple K Mi max on them and they still look new. Loss of traction on dry roads scared the crap out of me so i went back to the 402's that i had used the 1st 50k mi on the bike. For me, the traction tradeoff for increased tire mileage was not worth the risk

 

My stock Dunlops did this after a while. Went away when i changed tire brands.

 

I would expect that if the bushing were shot enough, the drivetrain could hit the chassis somewhere casing a growl.. I think that alignment would have to be way off to cause contact.. If the rear rubber isolators were all torn up, I'd expect the bike to handle like a drunken camel.

 

Rear tire.......been there, done that.

 

It's his passenger. Heck, mine growls regardless of which way I turn. Sometimes she growls in a straight-away.