Engine has a strange sharp noise, should I be worried?

[bulkwarrior]

Hi I got a 06 X5 4.4i with a N62 engine. Recently I noticed when the engine's running there's a high pitch tone which wasn't there before. It's not very loud, can't hear it at all from the cabin, but when you open the hood it's pretty obvious. I wonder if that's something I should be very worried. This is an old truck now and if the engine breaks maybe it won't be worth to fix it. Is there any way I can upload a sound file like MP3 to this post? I have recorded the sound using a voice recorder. Maybe you guys can help me out and point me to the right direction. The thing I fear most is the timing chain. Read a while ago that the guard rail for the timing chain is made of plastic material and tends to break. Have anyone replaced the guard rails? Is this a DIYable job or must be done in the professional shop? How much it would cost? I can also try to sell the car now but I feel unethical to sell it unfixed.

Thanks.

Will try to find out how to upload the sound file later. If not I'll just shoot a video and upload to youtube since there's a youtube button here.

Happy holidays!