My PCSpecialist custom build desktop machine has been sat on my desk for @ 2 years, and starting to get a bit noisy, so time for a spring clean.
Sides off, graphics card out, CPU cooling fan off, case fan off. Left PSU in place.
Crevice tool on the vacuum cleaner, and old camera lens brush, loads of dust/human cells! Used a straw on the end of the crevice tool for awkward corners.
All back together and quiet as a mouse.