Bicycle clicking popping sound felt in the pedals usually when pedalling hard
That sounds like something wrong with the chain. You may just have a worn chain that is skipping over the rear sprocket. I'd do a check of the whole drive train to rule all potential issues out.


Check for play or roughness in the pedal bearings
Check for play or roughness in the bottom bracket bearings
Check chainring bolts are tight, chainrings don't have any play
Check cassette / freewheel / rear sprocket for any play
Check sprocket and ring teeth for damage or wear
Check rear wheel axle for play or roughness.
Check chain for stiff links
Check chain for wear and elongation with a chain wear gauge