iPhone 4 Earpiece problem

Hello All

There is something wrong with Earpiece. i need to wait at least 5min then earpiece will work. i've changed tried changing earpiece and dock, same result. i've tried reset the phone. i've tried cleaning the two gold contacts and same result.

.....so after 5min of waiting. the earpiece will work perfectly all the time.

is it audio ic problem?

Thanks

Alan