While I would prefer if Sprites and their powers weren't necessarily affected by Noise, I do play that Diagnostics only works on things that are connected to the matrix. I think it is a good compromise against the folks who think Diagnostics is the worst cheese EVER (while fully exploiting all of the broken and overpowered magical mechanics).
Because it can only work with devices connected to the matrix, it may mean:
Devices have to remain wireless on. If you turn off wireless, Machine sprites "drop" the item and stops running diagnostics. Sprites have to re-roll diagnostics after devices turn back on.
Similarly, if ambient noise shuts off wireless, Machine sprites stop running their diagnostics. Implanted Noise penalty reduces can help wit this (datajacks/antennae).
If devices run silent, Diagnostics bonuses drop -2 down to 0 die bonus when using that device (limit bonuses remain).
If sprites aren't running silent (before rolling diagnostics, basically taking a -2 to their Diagnostics roll), their icons are perceivable with Matrix perception. Though their appearance is described as static garble that are not obviously sprites, someone trained in technomancer/matrix threats may be able to recognize the sprites as such (outing a technomancer or at least technomancer assistance). At the very least, someone checking might be curious about why there are extra icons hovering about your gear.
Diagnostics turns technomancers into adepts that can change-up their improved ability/improved potential powers, drawing on Resonance power instead of Magic, and affected by Noise instead of Background Count.