I have been wondering the same thing as I know that sometimes the filter pump drone sometimes annoys me when I'm trying to sleep, even though my filter is considered to be a quiet one! I'm only one month into my new fishkeeping hobby so I'm probably just being overly parental with my new babies
For background - I inherited my fish and tank from a neighbour who had to move out in an emergancy. The move was a disaster and traumatised the tank to the point half the population died
Since then the survivors (5 x Glass Bloodfin Tetra & 1 x Neon Tetra) have been constantly fighting and one dominant Bloodfin sits in the middle of the tank and bullies anyone that comes near it. The rest just sit each in their own corner alone and sulk. On a separate matter; I was also having trouble with the stream from the pump sinking all the flake food and driving it into the gravel before any of the fish could eat it - which was causing a large build up of rotting food.
As an experiment - I tried swiching the pump off before feeding so that they could get a decent chance of eating the food before it sinks. Instantly I noticed a change in their behaviour! The dominant Tetra stopped bullying and nipping. The loners came out of their corners. They started playing and investigating each other. They even started shoaling together for first time - even the lonley Neon was joining in!
I watched them like this for 2 hours then thought I'd better switch the filter back on - almost instantly they were all back in their designated corners with the dominant bully attacking everything nearby and the Neon sulking in a cave.
I have a 54 Litre tank and an Elite Stingray 15 in-tank filter (300 Litres/hour flow I think).
I did a water test and everything seems fine (Ammonia Nil, Nitrites Nil, Nitrates 40ppm, pH 7.9, Temp 27 oC)
Could the noise from the pump be effecting their behaviour? Maybe the water flow is too strong? Or could it just be purely down to stress from the death of half their social group? (or am I just being paranoid and reading too much into fish behaviour?).
(Sorry for the long post but I felt some background was needed)