An example would be Digitech Freqout on a daisy chain with drive pedals. The FO is a small computing device putting near constant noise to ground which..... can appear in the audio signal of drive pedals if in the same daisy chain. If the power supply is stressed (or the wall wart is starting to fail) the noise gets worse.
My drive pedals are all powered by one Caline style semi isolated 'daisy chain in a box'. The Frequot is powered by a completely different power supply - making for no noise.
Some digital pedals with time based effects can make clock noise / ticking noise which can appear if daisy chained - my Tardis drawer (all digital) - if I switch everything on (RV500, DD-500, RE-2, Dimension C, Mimic, MD-200, Freqout, and a Whammy located on the floor......and set the RV and DD500 to run dual presets..... the RV-500's tap tempo starts appearing as noise on the signal chain.... switch one thing off.... and its gone. The power supply is clearly nearing its load limit - not normally an issue as it sounded awful.
I'm planning on gradually upgrading the power delivery in my rack.