  Characterizing and understanding noise affecting quantum states has immense
benefits in spectroscopy as well as in realizing quantum devices. Transverse
relaxation times under a set of dynamical decoupling (DD) sequences with
varying interpulse delays were earlier used for obtaining the noise spectral
densities of single-qubit coherences. In this work, using a pair of homonuclear
spins and NMR techniques, we experimentally characterize noise in certain
decoherence-free subspaces. We also explore the noise of similar states in a
heteronuclear spin pair. Further, using a 10-qubit system, we investigate noise
profiles of various multiqubit coherences and study the scaling of noise with
respect to the coherence order. Finally, using the experimentally obtained
noise spectrum of the 10-qubit NOON state, we predict the performance of a
Uhrig DD sequence and verify it experimentally.
