University of Pennsylvania School of Medicine Feb 2 2026 Pink noise-often used to promote sleep-may reduce restorative REM sleep and interfere with sleep recovery. In contrast, earplugs were found to be significantly more effective in protecting sleep against traffic noise, according to new study published in the journal  Sleep  from the University of Pennsylvania Perelman School of Medicine.  The findings challenge the widespread use of ambient sound machines and apps marketed as sleep aids.