DTMF Tones take a while to play

I am working on a phone app. I have a dial pad grid view with buttons. I have a tone generator object created in onResume method. I also use a lock object. On click of any digit, i use the tone generator object to play a DTMF tone corresponding to the digit dialed using .startTone method. In onPause method, am releasing the tone generator object if its not null and setting it to null.

Facing following issues:

a) On the dial pad when i start clickin开发者_如何转开发g on buttons, first digit's tone is little low and it increases in volume for subsequent button clicks

b) If i go to another activity and come back to dial pad, and if try dialing digits, no tone is played for first 3-4 digits and it starts working fine after 5th dial onwards.

Need advice on solving this issue.

Thanks,