The fan is about to die.
Some people have dismantled their cards to oil the fan bearings but this is a temporary solution, these bearings are made with specially formulated lubricants and normal oils are just not up to the job.
There is two options:
Replace the card.
Replace the fan. Messing around with cooling fans on small cards is a pain, the easiest solution is to remove the fan, (not the heatsink, just the fan), and the attach a suitably sized case fan over the opening, either glue it or use cable ties to hold it in place.