As for only affecting the wireless signal...
it's luck of the draw as to wether it effects just the wireless, just the sync, both , or neither.
Any interference issues never fall into a hard and fast rules, all you get is a trend..
It's dependant on the signal generated and if soething in range is in tune/harmony with it.
As Soms said he wasn't aware of DECT's strong noise within 30cm, good, just means any combination of your set up aren't in tune with each other so no effect is noticed.