Well the tappet sound should not be too loud and Shud nt b present in all gears, its usually there when u accelerate in 2nd gear from a very low speed at which 1st gear shud have been used.
For a reference drive a CG125 and check its tappets sound.. CG makes ALOT!! of such sound.. and its normal for a CG.. Some engines are designed like tht.. and tappets noise is normal for them.
U need to only be worried if the noise is too loud.. Keep changing engine oil at time, use mineral oil and use petrol from a co. operated SHELL petrol pump.
nothing else.. the noise is usually a normal issue.
If the noise is too loud, take it to Suzuki ppl and ask them to set the tappets using the right gauge for it and set the gap correctly...
This shud do the job if tappets are the culprit.