It wouldn't hurt to get up close and see if one of the drivers is making the harsh sound. It's possible it's a bad driver.

As others have said, if you could reproduce the problem with a DVD soundtrack that would make troubleshooting MUCH easier. If the problem only happens on a broadcast then I would also cast a vote for it being a content problem rather than a speaker problem.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8