Could be a build up of wax, not uncommon. Two ways to go about this. 1 See doctor and will possibly flush the ear with some saline.
2. Over several days add a few drops of olive oil into the ear at night before sleep and block the ear up with some cotton wool, this turns the wax to liquid and drains as you sleep..
I used to be asked to do number 2 before all my ear operations.
However better to see the doctor first in case there are any underlying issues such as ''surfers ear'' Which is the body's natural defense mechanism of bone growth that closes in over the ear canal, normally from cold winds or or cold waster..
Dont use cotton buds as you can damage the ear drum permanently as well as push any wax further in.