  Ultra-Luminous X-ray sources are accreting black holes that might represent
strong evidence of the Intermediate Mass Black Holes (IMBH), proposed to exist
by theoretical studies but with no firm detection (as a class) so far. We
analyze the best X-ray timing and spectral data from the ULX in NGC 5408
provided by XMM-Newton. The main goal is to study the broad-band noise
variability of the source. We found an anti-correlation of the fractional
root-mean square variability versus the intensity of the source, similar to
black-hole binaries during hard states.
