I am not familiar with that COMM radio, but it might be a problem with SWR at those frequencies -- Has the cable, connectors, or antenna itself changed recently (become damaged, etc.?)
An easy thing to check is the SWR on the antenna/cabling -- see MFJ 259-D as an example test unit.
Retired Firmware Guy and Airplane Builder
2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231
Aided and abetted building a number of other RV's.