Just by digging the mystery of Mantras. I find that the vedic mantras, shabri mantras, etc, are Keelet (something which stops mantra to its power), and to gain full power of a mantra, the Utkeelan is necessary. Durga-SaptSati, a book dedicated to Goddess also talks about Utkeelan, but things aren’t completely clear. I think the jagrat mantras (which one takes from a competant guru) have utkeelan, maybe the reason that’s why they start generating vibrations …

Not only mantras but the yantras are also Keelet, though the yantra like Sri Yantra is not considered Keelet.

If anyone of you, know about Utkeelan, please do share something. Whenever I know about Utkeelan, I’ll update here.