My flat screen tv is constantly beeping even if it is off

Fault to the main power supply regulator section. Either it will be a separate board, or the part of main board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Pull up older posts.
http://electro-medical.blogspot.com/

It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.

There is an overload inside any one board in your TV. This type of fault is somewhat difficult to detect. it will be best to contact any service technician.

air cooler?..this is TV category..

Unless you oddly have a key stuck on your keyboard (which will make this sound), the constant beep usually indicates that the CPU fan has failed and the CPU is overheating.. check that it is working ok and if this is not the case, please repost.

There is a Diode and probably a Resistor blown on the power supply board... Check out the fix on my website:

http://normsweb.com/tektips/technika.shtml

I hope this helps you.

www.lg.com/us/tv-audio-video/pdf/47LG50_spec_sheet.pdf
http://elektrotanya.com/lg_lcd_tv_la84a_mfl41370007_47lg50-ua.pdf/download.html
Above user manual top, below is your service manual, perform the troubleshooting procedures and you should be able to localise your problem.

See if there is a plug under your driver's seat that is unplugged. Can you remember shoving anything under the seat that might have caused it to come unplugged?

Depending on the pitch. humming noises are either a motor ie: fan motor or if it is very low a defective capacitor . Since you have the yellow band and the high pitched beep my fist thought is somthing defective in the power supply. Take it to an authorized servicer.

some flat panel tvs are very tempermental like this...your best bet is to call the customer service number for your tv and ask them what to do.

call Toshiba ASAP if you still have warranty, the TV needs to be replaced. The line will get worse!!