Water pump going nutz

[Mrvile]

My Laing (Dangerden D4) 12v pump has a regular hum to it. However I notice that it sometimes changes its pitch, like it'll go lower for a second, then back up to normal again. It just did it real bad (like wuuuuuuuuuuuuuuuOOOouuOOOOOooOOouuuuuuuuuuuuuuuuuuuuuh) and I hope this isn't a bad sign or anything...

 

[IGBT]

..debri in the water?? scale accumulating? Do you have to put something in there to keep alge from forming??