33 Harsh noise

[Kpar]

Will it's always had this noise since I purchased it. Over a few years it's had a rebuild of motor, gearbox, rear axel,& several other mechanical repairs & noise always stayed the same. If I punch it up to 55-60mph the noise (grumble) stays there until I back off a bit & cruise at 55 with no load.
I've tried to compare it to Lawrie's which is a lot quieter even with his larger engine.
Maybe I just remove my Hearing Aids
Kpar