Often it's a water ingress problem on and around the aerial housing and connections; take off, clean up and / or replace, reconnect and remount ensuring a water tight seal.
Hello there and welcome along :tu Have you had a look in the dealers / garages section? I currently use the dealership but I'm now leasing so it's part and parcel but for my wife's car I use a recommended, trusted local garage far better service and cheaper, with folk that know what they're doing an...