> which would threaten their CE mark on the product.
Unfortunately the CE marking scheme is not as good as (for example) the FCC scheme, mainly because it's possible for manufacturers to self-certify their own equipment.
A responsible manufacturer will submit samples of their product for testing by a third party test house, who will issue a report to the effect that xyz meets standards a,b&c etc
Irresponsible manufacturers will just buy the little stickers.
Once while testing a computer for compliance we found that some of the test equipment we were using was itself radiating in excess of the applicable standard!
The CE mark is meant to mean that the product meets all applicable EEC standards. For electronic equipment I believe this now also includes a standard for susceptibility to interference from other sources. Perhaps the problem is the GPS Rx not the Radio.
You could try asking both companies for copies of their test reports but don't hold your breath. Even if they have them I suspect most companies will just ignore such requests unless you want to buy 1000's of sets.