My bike Crank is making noise like Tuk, Tuk... once or twice when I pedal hard I get a sound from my crank as if something were about to break to pieces when I stand and pedal hard.
The fault turned out to be a crippled ratchet in my rear hub. I got it replaced but am thinking of replacing my old bike now, it served me 10000Km in every season, every road in 2 years plus 3000Km in 3 years, a good service.