Squeaking tv i turn on my RCA tv, and after it warms up it has a high pitched squeaking sound. it sounds simmular to a high pitched dog wistle

If you have an AM radio/ other electronic device that is not well shielded close to some TV systems, it can also cause this type of sound in Stereos, turntables, computers etc... a lot of the time it is really easy to track down.
OR
You have a bad electrical ground in your apartment/House that needs to be checked quickly. Feedback is rarely a good thing!

P.S. you should always have your electronics all running off of the same ground via a surge protector of some type.

Hope this helps