Stereo and Fish tanks - noisy need help

Agreed, a canister type of filter like Eheim can be very quiet if maintained.
Also under gravel filters depending on how the tube feed is supplied.
I didn't see any mention of what you're using.
Fresh or saltwater? My big salt water tank was dead quiet. And went on for years and years til I moved...
Good luck... Easy to sort.

Bob, I have a 72 gallon freshwater bowfront between my speakers and it is very quiet. It is also beautiful and I'll bet your 240 is magnificent. The other posters recommending Eheim canister filters are on the right track. Those can be quiet and are also a boon to fish health so you have nothing to lose. I happen to use a different brand-Fluval-but either one is great. A 240 might take two of them "in parallel" (like two Eheim 2075's @ $300.00 ea) plus I would add a hang-on-back Marineland filter with a Bio-Wheel. A quiet way to gain valuable surface-breaking aeration for your pets. Expect to tweak vibrating plastic parts and add self-adhesive dots in strategic locations to control other 60Hz vibrations. A quiet tank is achievable although it might take a bit of work to get there. Totally worth it. I've had a big tank between my speakers since the mid seventies.

What kind of fish are you keeping? I was going to build my aquariums into my stereo room but was afraid of the noise and left them outside the entrance in a kind of fish lobby room.

The biggest canister filter that you find is the FLUVAL FX5. It's rated for up to 400 gallon fish tank. I don't know how quiet it is. You can search an aquarium forums.

Everyone thanks for your suggestions. I guess there is hope for a quite tank. Eheim & Fluval will be checked out. Any other recommendations?