Poor DAB / FM Radio Reception can be caused by items in the vehicle. For example some phone chargers give out a lot of interference that then can impact your radio signal. On occasions a Dash cam can cause interference. If the vehicle has poor Radio reception it’s worth unplugging anything you can see plugged into cigarette lighter sockets first to eliminate that aspect.
If the vehicle has a dash cam, unplug the power source to that (ideally at the fuse box / cigarette lighter end) to see if the reception improves, if it does plug the camera back in, bit by bit like reconnect the power lead (whilst physically unplugged from the dash cam) first and see if the interference is still gone, then plug in the dash cam until the interference is back so you know what part is causing it. If the Dash cam has a rear camera too it’s worth unplugging that from the front camera to see if it’s the rear half causing the issue. Then again plug the cable back in but disconnected from the rear camera end until the interference starts again.
Once you have identified which part the interference seems to be coming from you can try a few things. For example re-routing the power cable to the dash cam the opposite side of the vehicle may help, same for the cable to the rear camera if it runs down the drivers side, try it down the passenger side as on occasion it’s the proximity of the dash cam cable to the Antenna cable of the car. Otherwise you can try Ferrite Clips, if you try this try and loop the cable through twice like below:
Others have had success wrapping the offending cable with a Aluminium Adhesive Tape like this Screwfix and then attaching an earth to the tape. Usually the interference can be improved with these methods the annoying part is everything is trial & error!