I have been also recently experimenting with silencing the deadly noisy avalons. I have found out that if you live in a cold country ( for example in Sweden now the outside temperature is just 3 degrees), you are lucky and dont need to do much.

Here is what I have done to noise solution: Although avalon 741 has only one fan, you can still be able to put a hose to both sides of the miner, and it makes the fan work a slighty bit higher (in my case only 10 percentage points), but the total noise reduction will be around 20 dBs. The hoses I have used were both fire safe and highly sound-proof, surrounded with extra insulating material (a yellow woolish material with soft texture). I have put the intake hose to outside through a small window to take in cold air, and have put the longer hose to inside to heat my room. The longer the hose, the better the sound-proofing, so its a good idea to put the longer hose to the front of the miner, rather than the backside, because it is farther away from the fan. For further noise reduction, you can tape the small cleavages around the miner fan to reduce noise passing through