First of all , find out what drive you have. When you take your xbox apart, look ontop of the DVD drive and read the label and if it only says benq, then you have a benq... if you see somewhere a "phillips and lite-on digital solutions corporation" then its a lite-on.
Go on ebay (or here) and buy either a new DVD drive (best option IMO) or a new laser. Replacing the laser isnt that hard, but you could screw something up.
You need to buy the same brand DVD drive as the one you have, which is most likely a BENQ or LITE-ON going from your post.
The lite-on and benq dvd drives are very quiet, the reason yours maybe loud is because the laser is having trouble reading discs so its just going nuts.
When you get your new drive, take the 4 screws off the bottom of it, and take the top and bottom shells off. You should see a little black plastic tab holding the board in, bend it to the side and carefully tilt the board up. Disconnect any cables you see going to the board (use your fingernail to pull up on the little clip holding them in) and remove the board....
Put your board from YOUR DVD drive into your brand new DVD drive (one you ordered), put the cables back where they belong and put it back together and plug it back into the 360.
I think thats everything