Got a 2003 VW Diesel Golf, with 101,000 miles. Had the timing belt and brakes replaced at 90,000 miles and at about 97,000 miles the car started to run noisy . We checked the oil and it was low, and probably had been for a while. Adding oil did not help. Last oil change was also at 90,000. (VW recommends changing it only every 10,000 miles. obviously we should check it more often)
The noise is definitely coming from under the hood, and you can feel vibration in the steering wheel. It is most noticeable at low speeds. When idling, there is no noise at all. At high speeds the car sounds almost normal, but a little loud.
Took it to the shop and they performed an oil change at 100,000 miles. They did not hear the noise and told me it was probably just that I had let the oil get too low. Their oil change did not fix the problem, however.
Any idea what it could be, before I take it back to the shop? Thanks!
A bad injector can cause noise that will override any of that diesel noise. It will also cause vibration.
The way this should be checked is to slightly loosen the fuel line at the injector while the car is at idle. If the noise goes away the injector is at fault and needs to be replaced or rebuilt.
They should be checked one at a time and the loosened line should be retightened before going on to the next injector.
As to checking your oil, you should do this every other week at least.
How low was the low oil? If it was still showing on the dipstick, likely there was no damage. Yes, check oil at every fill up, which is about every 600 miles on my TDI. Without hearing the noise it is rather difficult to figure out what it is. Heat shields, engine mounts or a hundred other things. I doubt if the noise is related to the oil issue, but it is possible.
Is that shop a dealer or who. If it is a quick oil change place, run away from there, and expect that they used the wrong oil for your TDI. Even dealers are known to use the wrong oil. That 10,000 miles is OK for that engine, but it does require the right oil.
My guess is going to be a timing problem that resulted from the timing belt change. It is not all that unusual. You need to find someone who really knows that car. Try http://forums.tdiclub.com and look around or ask there about a local mechanic who can give you a hand.
You know how the picture for the dipstick bends and shows zones A B and C? Ours was just below zone A, below the dent. Adding a whole quart was too much. The shop was the local dealership. I really need to find someone good and local so I stop getting overcharged. 
The dealership was also the one that did the timing belt. I remember hearing on the May 31 Car Talk about the guy (I think it was the Dean of a church?) whose timing belt jumped off its teeth, and I thought that definitely sounded like it could be us, given how recently we had the timing belt worked on.
Of course, it could also be like ok4450 said above and be the injector… Although I hope not - that sounds expensive.
The TDI’s been such a good car for us so far! Drives great in the Syracuse snow and we’ve had very little trouble with it. Thanks so much to both of you for your advice!
Took it back to the dealership, because they did the timing belt… And they said it was a front left wheel bearing.
They fixed it, and now it’s louder than ever. They did, however, say that my tire was pretty chopped up so they moved it to the back. Said I would notice some noise until the tire wears in more evenly.
At low speeds now, the car just ROARS. If you jerk the steering wheel to the left, the noise disappears. I’m taking it back on Thursday. Is it just the back tire, or did they do something wrong?