Problem Solved: Once the mechanic replaced the correct fuel filter (took me twice to get the right one!), the car stopped making the noise. The filter was so clogged and my mechanic suggested to just change it every 30,000 miles even though his book says 60,000 miles. The fuel pump was easily worn because of the filter.

I would suggest to people with this same model to at least have your fuel filter checked every 30,000 miles and if you are buying a used one, VERIFY all of the maintenance done on the vehicle either before or during signing if it is available.

For everyone who helped me, I would like to say thank you.

 

Fuel pump and fuel filter. Filter causes pump to work harder and make noise. 60k is enough to get it clogged.

 

I own a 2004 Audi a4 1.8T. The noise started out quite then grew louder and more intense over a few months especially when it was hotter outside. (Not sure if the heat had anything to do with it). Anyway I took a look at the fuel filter and I noticed the file line that is used to connect to the filter is kinked! There are four limes that connect to the filter, two going in and two going out. CHECK all four of the lines for kinks! This will cause back pressure for the fuel pump and cause it to whine or emit the high pitched humming noise. Some of the lines can not be un-kinked due to the material the line is made of and must be replaced. I had to buy 3/8s rubber fuel line form O'rileys and then hose clamps from Wal-Mart to put on each end of the 3/8s rubber fuel line to tighten down on the existing line then to to the filter. ONCE THIS IS COMPLETE check and see if the noise is gone. If not fully gone or gone at all then replace the fuel filter. I bought the cheapest one from Amazon for 31 bucks and free shipping. Made in China but who cares. This should be all you need to do. If the noise is still there! Then it's your fuel pump. But I just did the first two steps for my car and it works great and it perfoms much better now that it is getting proper fuel flow. Hope this helped.