suburban furnace problem

if its belching exhaust into the trailer its no good the heat exchanger has a hole in it allowing carbon monoxide into the trailer

Yep-- bad heat exchanger, have had that happen in the distant past on our 1st Class C.

.... low humming noise and it also vibrates.......belches exhaust back into the rv through the vents


RV furnaces are sealed units......combustion side is separate and sealed from room air side.

You should not operate that furnace again until it has been pulled, inspected and repaired or replaced.
Belching exhaust into room side (thru registers) is allowing combustion by-products into inside of RV.
Carbon monoxide is a toxic gas, but, being colorless, odorless, tasteless, and initially non-irritating, it is very difficult for people to detect.
THAT IS DANGEROUS and can KILL

Pull it and replace. It's burned through and is history.

I would also stop using it but by it humming it sounds to me like the fan is fowled and the vibration supports that as in clogged on one side of the fan cage. the furnace may not be a total loss but,BUT you will need to pull it at any rate and inspect all the components and especially the combustion chamber as mentioned above. Do a diligent job and clean everything: fan, burner,pilot if it has one.A replacement may be more cost effective than repairing an old one but I have found parts on E-Bay for mine. good Luck!