Pump Noise - Backpressure?

[purklize]

It didn't happen at first. I have a big air pump that can connect to up to 8 air stones, but I have it only connected to two at the moment. Two more air lines are open, four are blocked (out of eight total). I think it might be because of the pump not having an air filter, and the air stones clogging with dust, because when I swapped in new air stones it was somewhat quieter. I'd only been using those air stones for 3 months though....

 

What should I do? Any suggestions? I can muffle the noise by piling blankets on it but then I have heat problems; I can blow a box fan on the mountain of blankets but then I still may have a backpressure problem. I don't want to destroy the pump and come home to find a dead garden.