Humming Filter

[Bugdozer]

I have a trickle-style filter in my tank, which has worked great with no problems since I got it in May last year. In the last couple of days the motor section has begun making a noticeably louder hum (it used to be very quiet indeed). I have never opened it up to clean the impellor unit, do you think this could help, or is the problem caused by something else? It's still pumping water just as well as it used to as far as I can tell.