Ok, so given both 60 and 40 share the same rx filter then I wonder if the fault is inducing noise from elsewhere in the radio due to a fault.
This could be a solder bridge, dry joint or any of the usual faults we put in when building a radio : )
The LPF forms part of the RX chain, it would be worth checking that, or even swapping LPF's between 30 and 60/40 to see if the fault moves / changes.
Warren.
