We undertake a study of M51 ULX-7, using archival data from XMM-Newton, Chandra and NuSTAR, and optical and radio data from HST and VLA. The source has a consistently hard powerlaw X-ray spectrum with Γ˜1.5 and has high short-term variability, with all XMM-Newton observations having 30-40 percent rms. This is unusual variability behaviour for a ULX as we would expect highly variable ULXs to have soft spectra. The power spectrum features a break at ˜10^{-3} Hz, from low frequency spectral index α=-0.1 to high frequency spectral index α=-0.8, analogous to the low frequency break found in power spectra of black holes accreting in the low/hard state. We do not observe a corresponding high frequency break, however taking the white noise level as frequency upper limit, we can calculate a black hole mass upper limit of 9.12×10^{4} solar masses, assuming that the ULX is in the low/hard state. While there is no radio detection, we find a flux density upper limit of 87 μJy/beam. Using the X-ray/radio fundamental plane, we calculate a black hole mass upper limit of 1.95×10^{5} solar masses. Therefore, this ULX is consistent with being an IMBH accreting in the low/hard state.