Samsung PS50P91FD crackling noise. I recently purchased a Samsung PS50P91FD 50 in plasma and when

Question

I recently purchased a Samsung PS50P91FD 50 in plasma and when turned on after approx 15 minutes it makes a crackling noise from all around the front of the screen. Sounds like the front plastic cover? I think it may be heat related? Is there a way to fix this? A Samsung tv technician came around and said it was the first time he encountered it and that there was nothing he could do.He said it was a physical problem. He opened the unit and tightened all screws but the problem sounds like it has worsened. I opened the unit and loosened the screws but the noise still persists. This is the second tv as the retailer i bought it from exchanged the first one as it had the same problem. Any help please?