Hissing from speakers

Hi - on my 2nd replacement N95 and beginning to despair. Fully charged this morning and by lunchtime was down 2 bars with a few texts and some video. I expect this to improve however with a few charges. Problem I had was I made a call and when I ended the call a few minutes later I noticed a faint hissing noise. Holding the phone to my ear I noticed it was coming from the speakers on the phone. I didn't have any programmes loaded so turned off the phone and turned back on - hissing gone. Anyone else had this? I really do not want to send this back again as I now at the end of the road with this phone. I love it - does everything I want and can't imagine getting anyother phone which will beat this. Thanks again for your help.