Noisy fan due to wall vibration; Sorbothane pads

[ghatfield]

I am in the process of replacing a 12 v Hella fan we had in our 19' Bambi (2006). We have only had it for a few years and it had light use but the base of the fan blade cracked making it noisy.

We bought a Caframo 757 fan to replace it, but it is also noisy. This time then noise appears to be due to vibration from the fan which is transmitted to the wall it is mounted on. See the attached photos. When the fan is not mounted it is very quiet. I had thought about using Isolate It (Sorbothane) pads, but they contain a plasticizer that will discolor wood and I don't want that.

Question: Suggestions to reduce the noise?

[ghatfield]

First, let me say that the Hella fan is a lot quieter than the Caframo fan 757 when they are mounted on a plywood wall. The base of 757 bracket rests against the wall and this efficiently transmits any vibrations from the fan to the wall.

I tried putting some furniture pad material between the fan and the wall. No help.

I tried using through bolts rather than screws into the plywood with the holes for the screws lined with a rubber grommet on both sides (see attached, similar to those shown). No help. The screws transmit vibration into the plywood.

The only way I found to reduce the noise was to not have the base of the mounting bracket resting on the plywood. I did this by using rubber grommets which hold the fan away from the plywood about 1/8" and line the bolt hole with rubber. I also used rubber grommets on the inside surface of the bolt hole along with the furniture pad material (see attached). It is still not as quiet as the Hella was, but it's not bad.

I would welcome any suggestions to improve this installation.