Clutch making noise

Hi

Thanks for this post, I have just bought a car from a second hand dealer, I noticed when driving when I push the clutch pedal in to change gear it makes a pop noise and won't go into gear, this only happens now and again usually when going into 2nd gear, I've done about 150 miles in the car and it's happened like 8 times. It made me stall at the lights because the clutch made the popping noise and wouldn't let me change gear. Have you heard of anything like this happening?