What you have is actually very common in your model, in your set you have what is called a color wheel, the bearing in this goes bad and starts making this noise you are talking about. The only way to fix this is to have the color wheel replaced, if you decide to have this done professionally you will be looking at around $300-400.
If you have electronic repair experience and would like to attempt this yourself let me know and I can get you some information on completing this task. However I will warn you, I have seen many consumers like yourself destroy their set when they attempted a repair that should be left to a professional. But if you have experience and think it is something you can do let me know and I will help!
I am sorry I didn't have a quick fix for you on this one, please let me know if there is anything else I can do for you!
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