Hey buddy, I also use the record function extensively, didn't happen to me yet. Can you just pop over to Settings>Sound>Volumes and check the volume levels there. If it is at proper levels. If thats not the problem, you may want to do some tests.
- Go to dialler and type *#*#2486#*#*
- Click on 'Start CQA Test in Menu Mode'
- Go to Audio and and do all the tests.
If all are working fine, and you still have that problem, its the time to call the customer service.
Hit Thanks button if I've helped