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.
