sounds like a motor or transmission mount is your likely problem
bad synco rings
check the fluid in the rear end it might be dry causing medal to grind causing a clunk noise or the gears in the rear end or worn done causing it to do the same thing
YOU WILL FEEL A CLUNK WHEN THE VEHICLE IS PLACED IIN REVERSE OR DRIVE AND IS ACCELERATED WITH THE BRAKES DEPRESSED
Worn trans or diff parts. If it gets worse, have it looked at.
Worn CVC joint. Could be bad struts causing the spring to bind. Depends how severe the clunk is. If it is struts, it sounds like the floorboard is getting hit by a sledge hammer.
when you change directions from forward to reverse it makes a clunk sound and there is a slit delay in movement.
Pull the rear wheels off and check the brakes. Something may have broken or fell apart.
it could possible be the U-Joint which is a cheap and easy fix. it's connected to your drive shaft.
it may be the rear tranny mount
If the ticking is in time to wheel speed and most noticeable on turning I would suspect an outer CV joint. An inner axle joint might clunk when shifting into reverse. Maybe they're on the same axle. Other possible causes of clunking are worn-out motor mounts.
You're a clunk-head...
Your bike may clunk when you pedal hard due to issues with the chain, gears, or bottom bracket. These parts may be worn out or not properly lubricated, causing the clunking sound. It is recommended to have a professional inspect and repair your bike to prevent further damage.