why is my Honda inova 125 making a lot of noise?

[GaryLDN]

I recently Bought a new battery as mine died , was stalling and electric start had gone eventually wouldnt start. Fitted a new one (YTZ75 if that means anything to anyone), it starts like a dream and no longer stalls at all but it makes a racket constantly popping especially when i release throttle in 3rd , is this normal with a new battery ? its like a splutery popping sound lol ,, im not good with bikes only ride one for the Knowledge of London , Thanks in advance