Do you get that noise with no fan too or just with the fan on? Fans are an easy do it yourself fix.
Go-Power has somebody make their inverters, which may have changed since 2006. (Xantrex used to have a 1750w MSW inverter that was re-branded by several others, eg.) You can ask Go-Power (Carmanah here in Victoria) tech support about it.
Inverters have come down a lot in price since 2006 especially if on sale, so it is not a killer to get a new approx 2000w MSW for under $200
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.