Hi JJ, I posted this on the other thread but thought I would post here as well for anyone searching for M4 interference. The M4 is the main culprit, PC can be generate some but to a lesser degree and finally any device with an SMPS, such as a (some) cameras. It's a pain to have to go the expense and hassle of fitting the PSU into a correctly RF screened case, and even then placement and lead dressing around the PC are still important.
It's not going to be easy to find a PSU that is (truly) free from radiated interference. You really need to find four or more people with PSU brand X that are running DAB-FM and GPS and have tested reception using a laptop (PSU on and off) out of the metropolitan area where reception is not saturated with DAB-FM signal levels. I have seen people fluke an installation with an M4 and have no reception issues in their location. I have technically proved beyond any doubt that the M4 is a noise generator, but so too are most SMP supplies, it just comes down to how much they produce.