Ok,
Adding thin duct insulation along the walls of the blower enclosure has helped to reduce the reasonance that causes the hum on the steel enclosure. But most of it was coming from the two flanges where the blower mounting plate bolts into. I added both felt and self stick weather stripping in these areas and I manage to lower the reasonance by about 50% and a more acceptable level. However, I did notice that the blower wheel needs to be changed as there is a lot of rust on the vanes and this may also contribute to the noise level. So I will place an order to replace it.
Adding thin duct insulation along the walls of the blower enclosure has helped to reduce the reasonance that causes the hum on the steel enclosure. But most of it was coming from the two flanges where the blower mounting plate bolts into. I added both felt and self stick weather stripping in these areas and I manage to lower the reasonance by about 50% and a more acceptable level. However, I did notice that the blower wheel needs to be changed as there is a lot of rust on the vanes and this may also contribute to the noise level. So I will place an order to replace it.
