The only rules about noise is:
Noise represents any interference between a user and their target. Noise can be created by sheer distance or other factors, such as jamming or obstructions. Each point of noise incurs a –1 penalty to any test taken in the Matrix. If noise is greater than the device rating, the device cannot access the Matrix or provide wireless bonuses.
So technically, Noise represents the noise "between" to points, not "at" those two points. That's not really clear. Maybe you just take the higher of the noise ratings?
So let's say Becca the Decca is in Downtown Seattle, a Rating 4 Spam Zone.
She is using a DR 4 cyberdeck, and the noise is very nearly enough to knock her cyberdeck offline but she manages to slice through the bloatware.
Her target is the commlink of a VIP inside a corporate office, who is currently in his office on the 44th floor of the corporate headquarters. This puts him roughly 130 meters up, enough to introduce 1 level of noise due to distance.
This doesn't mean that Becca's deck will be knocked offline, only that she will face a -5 dice pool if she tries to hack from her current location. She could run Signal Scrubber to drop that down to -3, or try to get into the building to both reduce the Spam Zone rating and maybe even get up a few floors to eliminate the noise level due to distance.
Now, let's say the VIP wants to hold a confidential meeting. He fires up his Rating 6 jammer, which is not set to exclude anyone. In other words, any device of level 5 and below in a 10 meter radius will be knocked offline. If there is background noise on the 44th floor, it could even knock out devices with higher ratings because jammers could potentially contribute to local noise like spam and static zones; this is not clear.
If his commlink is knocked offline, it is now completely impossible for Becca to hack her target.
If, on the other hand, he chooses to exclude his own commlink so that he can keep sending lewd messages to his assistant while everyone else in the meeting has their devices knocked offline, his commlink would still be a valid target. What's more, the noise introduced by the jammer is not strong enough to penetrate down to the ground floor (130 meters away) where Becca is still loitering. So the jammer has affected the local area, just like a Spam Zone, but not Becca's attempt to breach the commlink.
For the most part, this makes sense, but it does make it a little tricky to wrap one's head around where noise is calculated and how. Or is that just me?