Noisy Fan

Hi, I have a hp a1223w desktop computer and the fan is getting quite noisy. I have cleaned it up, but it is still sounding funky. I was just wondering how I go about finding a new fan for this thing, it is pretty old and not sure how to find out if one is compatible with my computer.

Do you have a guess as to which fan is noisy?
It could be the power supply fan, in which you replace the entire power supply.
Or if could be a case fan that generates air flow. They are low cost and are replaced by removing four screws. You just have to be sure the power plug or socket is a two, three, or four pin, then buy a new one. Sometimes the power plug is the greatest difficulty.
CPU fans are more work, and it is wise to replace the entire heatsink and fan as a set. There are risks in doing this. Some heatsink hold downs are made of plastic or other materials that can break.
A lot of local vendors, as well as online vendors such as Directron, Frys, Krex, TigerDirect, NewEgg, and others will have what you need.
The secret usually is to avoid cheap products. The units which are quiet and have the best bearings and best fan blade design to reduce noise while moving a lot of cooling air, will cost more. As with all other computer products, some brand names are better and can be trusted. If it is cheap, it probably cannot be trusted to be quiet, although it make work ok.
There are reviews on-line for CPU fans, but case fan reviews are scarce.
There is a great deal of design work in moving air. The cost is usually worth it.